Information and expertise on plastic product design
What is Plasticprop?
A properly designed plastic product is functional, durable and thus environmentally friendly. Unfortunately, 7 out 10 of them fail prematurely. In most cases, failures could be avoided by better design, including the right choice of material.
Plasticprop.com is intended for sharing knowledge and experiences on plastic product design among professionals, both green and seasoned. Please join the conversation and share both your questions and insights.
Let’s make better plastic products together!
Plasticprop material selection guide
It is essential for your component to be transparent.
When you need your product to be transparent, your choices are limited mostly to amorphous plastics. You need to address their common weaknesses. In general, amorphous plastics are not well-suited for machine design purposes.
PP Random Copolymer, PP-RC, is the only semi-crystalline exception among the amorphous alternatives. It is always at least slightly milky but has many advantages (chemical resistance, ductility, use of integral hinge) most of the amorphous materials do not offer. Some PA6 grades are also translucent, but can not be described as transparent.
The most common and best known transparent plastics are PC, PMMA and PS. PC is known for its exceptional impact resistance, PMMA for its glass-like clarity. PS is an affordable commodity plastic, familiar from CD-cases.
The Material selection tool presents the following transparent plastics:
Examples of applications
Optically good plastics have replaced glass materials in many applications, especially in the growing led light industry. They are easy to process and lightweight.
The housings of car headlights are primarily made of PC, protected with silicate lacquer for improved UV resistance.
Poor chemical resistance is another disadvantage of PC. Lighting covers in agricultural use are rather PMMA than PC due to its better resistance against ammonium fumes.
Motorcycle visors, police riot shields, safety goggles, or whatever requires extremely good impact resistance, are made of PC.
In long term outdoor use, the products are painted with silicate lacquer for improved UV resistance.
FDA approval Copolyester is a common choice for sport bottles. It is clear, impact-resistant, and FDA compliant.
Copolyester is widely used in baby-bottles as well.
Refrigerator boxes are made of commodity plastics PS and SAN. The thickness of their walls is often inadequate which makes them break very easily. Using SAN instead of PS (better impact resistance, slightly higher cost) and increasing wall thickness would make the boxes more durable and therefore more sustainable.
The lids of the boxes are often made using the same materials that have been colored opaque.
Transparent components in the process industry often require good chemical resistance, good thermal resistance and good long term resistance against hot water or steam. This is is why amorphous high-performance plastics PSU, PPSU, and PES are used. They are often used even when transparency is not required.
Depending on the case, amorphous PA12 might also be considered.
What do you need from your product?
The most impact-resistant transparent material by far is PC.
PPSU is the best choice in high-performance materials.
Wall thickness has an effect on the impact resistance of a component. The transparent side-plates on the ice-hockey rink are made of thick PMMA plate. Avoid sharp inner corners whenever you can.
When operating in a cold environment, plastic components tend to become harder, stronger and stiffer. However, they also lose some of their toughness and turn more brittle. This will affect their impact resistance.
Strength and modulus
Stress-at-break values for common transparent plastics in room-temperature are between 40-70 MPa (PP-random-copo ~20-30 MPa ). From a durability point of view, however, impact strength is usually a more relevant factor than tensile strength.
Transparent materials like PS, PMMA, and SAN have a tensile modulus of above 3 GPa at room temperature. MABS, PC, SBC and copolyester are closer to (below or above) 2 GPa. The difference can be heard if you knock the product with a teaspoon; the higher the sound, the higher the modulus.
Higher modulus usually leads to lower toughness and therefore lower impact resistance.
Please remember that elevated temperature has a significant effect on the strength and modulus of plastic materials. Ýou should not look at the value in room-temperature but at maximum service temperature.
PMMA is used in boat windows due to its good scratch resistance.
Despite its good ductility, PC is prone to scratching. Motorcycle visors are coated with scratch-resistant lacquer.
Performance in elevated service temperature
High-performance materials offer the best thermal resistance (above 150°): PSU, PES, PPSU.
Thermal resistance is one of the advantages of PC, up to 125°C. PC-HT goes even higher.
Amorphous PA12 can withstand 80-100°C in long term use, which is fairly high for a transparent material.
You need to establish the maximum temperature your product is going to be stressed in, choose a material suitable for that range and design the product bearing in mind how the temperature affects its mechanical properties.
In addition to short term service temperatures, you must also take into account that if the product is constantly (long-term) subjected to high temperature, creeping will speed up, and stress corrosion and, in some cases, thermal degradation will appear. Static loading and high temperature are an exceptionally challenging combination for plastics, especially amorphous grades.
Performance in low temperature
When operating in a cold environment, plastic components tend to become harder, stronger and stiffer. However, they also lose some of their toughness and turn more brittle. This is especially likely to happen when operating below the material-specific glass transition temperature, Tg. As amorphous plastics are used below their Tg, PP-RC is the only transparent plastic that can be used both under and above its Tg which is app.-20°C. Below that it is likely to turn brittle.
If your product is likely to be used in cold conditions, and especially if it is subjected to impacts, make sure its toughness is sufficient in the expected service temperature. Explore reference products to confirm.
In general, amorphous plastics have significantly lower chemical resistance than semi-crystalline ones.
PP-RC is the only semi-crystalline transparent material available and therefore a common choice for applications used in a chemically demanding environment.
Temperature, duration of the exposure and mechanical load are important factors. The lower they are the better.
Fluoroplastics are the only material group than can be considered inherent to UV light. With all other plastics, UV light is an issue.
UV stabilized grades of practically all plastic materials are available. Choose them in order to extend the lifetime of your product.
Transparent materials with poor UV-resistance include PS, PC, MABS, and copolyester. Car lighting components are commonly made of PC, a material with relatively poor UV-resistance, which is why they are dipped in lacquer.
Resistance against water, boiling water, steam
PC is prone to hydrolysis. It might degrade in long term contact with hot water.
If the component is constantly exposed to hot water/steam, high-performance materials like PSU and PPSU should be considered.
You are designing a commodity product.
- Go back
If your requirements for both appearance and mechanical performance are low, you are likely to find a suitable material from the lowest level of the plastic pyramid. These materials are typically known as commodity plastics.
Commodity plastics are inexpensive. Often, they have weaknesses in outdoor use, chemical, and thermal resistance or mechanical performance. Please take them into account as the low cost can not be the only defining factor in your choice of material.
Low cost does not necessarily mean that you can not produce a quality product. For example, ABS and PP both have many excellent qualities that enable both mechanically and visually pleasing outcomes when applied properly.
Commodity plastics include both semi-crystalline and amorphous grades. Every product has some requirements in terms of mechanical load and service environment, so as a reminder:
- Amorphous materials are more likely to provide a straight-edged result with a clean surface finish. However, the product may not be extremely durable in a challenging operating environment or if it experiences long-term loading.
- Semi-crystalline materials have better chemical resistance and mechanical properties but due to higher, more uneven shrinkage, the product can easily warp slightly.
Amorphous options include PS, HIPS, and SAN. ABS and ASA are also fairly inexpensive and often classified as commodity plastics. PVC is a common material in the construction industry but less used in consumer goods because of its poor recyclability.
When designing packages and other disposables, please consider how to minimize the amount of plastic, the possibility to use recycled grades and how to make the recycling of the product as easy as possible.
Examples of applications
A storage box is a typical commodity product. It requires a certain amount of strength and stiffness, but ductility is more important. Storage boxes are kicked and thrown around. A pile of boxes easily falls.
Often storage boxes are stored in cold conditions, and they should not turn brittle. If the box is packed full of heavy books, it should not be sensitive to stress cracking. This is one reason for favoring semi-crystalline plastics.
PS is harder, stronger and stiffer. Therefore one could imagine, that it is a better choice for a knife. PS, however, is brittle rather than ductile and it easily breaks if bent, which leads to sharp and spiky edges. From this perspective, PP is a better choice, although its modulus is low.
Today bio-based and biodegradable PLA is a common material for disposable cutlery. It is questionable how sustainable choice PLA is. It does not really degrade in nature unless composted at elevated temperature. Recycling PLA problematic as well. It can not be done as part of the same process as PS, PET, PP or PE.
Another growing material group is a composite of PP and natural fibers, such as wood, bamboo or cellulose. The benefits are in lower oil consumption as well as a stiffer product. The recycling process is not improved, though.
Unfortunately, the whole product is often made for single-use, even in the case of a 2K application. Recycling of metal, PS/ABS and TPE is not easy.
What do you need from your product?
If your product is used or stored outdoors, you have to take UV light into account. Prolonged outdoor exposure affects the color of your product and may turn it brittle.
All the low-cost commodity plastics, amorphous and semi-crystalline, are somewhat sensitive to UV light. ASA is commonly described as “ABS for outdoors” and often the best choice among amorphous plastics. Ask your material supplier for test data and compare it to your intended use.
PP is a better choice than HD-PE, although all general-purpose grades are somewhat sensitive to UV. Using both UV modified base material and colorant resistance can be significantly improved. As a reference, many roof ventilation products are made of PP and have long warranty times.
Color choice is an important factor also: the darker the color the better it blocks radiation.
Performance in cold temperature
In some cases, your product may be used in subzero conditions even if it has not been your intention.
ABS and HD-PE retain their ductility well. ASA with a better UV resistance has lower impact resistance than ABS in cold.
PP homopolymer has Tg around -10°C which is not rare in the Nordic winter. Below it, PP-H turns brittle. It may suddenly break under loads it easily withstands in warmer conditions. PP copolymer is a better choice, especially the grades that have been modified to retain their toughness in cold conditions.
Please suggest what property you’d like to have included.
You need a technically efficient/reliable material but not necessarily high strength or stiffness.
When designing parts with demanding technical functions, both mechanical and service environment-related, semi-crystalline materials are typically a good choice. Their ability to withstand continuous load, fatigue, wear, and lubricants are superior compared to amorphous plastics. Levers, gears, cams, wheels, pulleys, etc. are usually made using semi-crystalline plastics.
Amorphous materials (or an alloy of amorphous and semi-crystalline plastics) can be the best choice when the function of the product requires very high impact resistance or dimensional accuracy.
Technical does not automatically equal poor appearance. With proper design and appropriate tooling/process, the result can be visually very pleasing using semi-crystalline materials. Making amorphous materials withstand continuous load or chemicals is a harder task.
The most typical materials used in machine design are POM and different polyamide grades, such as PA6, PA66, and PA12. Other good options are from the polyester family: PBT and PET. In challenging conditions, semi-crystalline high-performance plastics, such as PEEK, PPS or PPA might be needed.
Examples of applications
Chain saw and lawn-mower housings
The housings of chain saws and lawn-mowers do not carry much weight but they must be tough and resistant to oil and gasoline as well as UV-light. They also need to have a relatively high quality appearance.
The plastic used is typically PA6/PA66.
ABS is such a common choice for lawn-mower decks, that manufacturers must have validated its chemical resistance to be sufficient.
Side release buckles, plastic zippers
Side release buckles require low friction and good resistance against fatigue and continuous load. These are all properties of semi-crystalline plastics, especially POM.
Due to the low friction properties, injection-molded plastic zippers are made of POM as well. Plastic zippers are also produced by “coiling” a plastic monofilament to form the teeth. This type of zippers are called “Nylon Coil” zippers, although PA is today mostly replaced by polyester, assumingly PBT.
Electrical connectors, relay sockets and switches
Compared to the other semi-crystalline engineering plastics, PBT offers the best dimensional stability. It does not absorb moisture as PA does.
If switches or relay socket require higher strength and stiffness, PBT may be reinforced with glass.
The materials used in helmets must have good toughness so they do not crack, and high strength to take the high load without deforming.
Helmet is a good example of a technical and demanding high-quality product that is made of amorphous plastic.
Ice-hockey helmets are typically made of HD-PE.
What do you need from your product?
The surface of PP, PA or POM is slippery, even oily, to touch. POM is the most common choice for low friction applications. Different PA grades are typical as well.
In demanding applications, polymers can be filled with oil or PTFE to achieve low friction.
Two important factors in your application are surface pressure (P) and sliding velocity (V). If P*V is very high, the surfaces will inevitably heat up. In such cases, semi-crystalline high-performance materials like PEEK or PPA are used.
In case you are planning to use amorphous plastic, it is highly recommended to study its friction properties beforehand.
High quality appearance
When visual high-quality is needed, designers often prefer amorphous plastics. If the mechanical challenges are limited to impacts and short term-stresses, common housing plastics, such as ABS, ABS/PC or PC, fulfill the purpose. However, if resistance against fatigue, stress-cracking or wear are needed, you are likely to find a more suitable plastic within the semi-crystalline offering.
When properly designed, the following materials can deliver pleasing visual quality together with mechanical performance and chemical resistance (in preference order).
- PC/PBT alloy
Compared to amorphous materials, semi-crystalline plastics have a higher and uneven shrinkage, which results in more pronounced warpage and sink-marks. It is therefore important to follow the basic principles of plastic product design: uniform wall thickness, sufficient radius, and rib thickness guidelines. From a tooling perspective, a well-defined parting line, proper cooling, and a properly positioned injection system are vital.
Fatigue is a phenomenon that plastic designers should always take into account. The effects of fatigue do not show in the short term use. A component might withstand 100 cycles with no visible effect but suddenly fail after 15 000 cycles.
POM is known as a “spring plastic”. It endures fatigue well.
All the polyamides are also highly fatigue resistant.
PEEK is a high-performance material but has excellent fatigue resistance at room temperature as well.
To avoid fatigue, a component should be designed so that the repeating stress is significantly smaller than the tensile strength of the material, approximately 10-20%.
Resistance to continuous stress
Stress-cracking is the most common reason for plastic components to fail their purpose.
Semi-crystalline materials endure continuous stress far better than amorphous materials. POM, PA, PBT, and PP are good options if long term stress is expected. HD-PE is an exception among semi-crystalline plastics, it is prone to stress-cracking.
To avoid stress cracking, the product should be designed to endure significantly higher stress than short term experiments indicate. Semi-crystalline materials endure continuous stress better than amorphous materials.
Resistance against hot water and steam
Amorphous high-performance materials, such as polysulfones PSU, PPSU, and PES, are typically used when good dimensional accuracy and high strength are needed under exposure to hot water and steam. They do not, however, are not a good choice for moving components of a mechanism.
- It doesn't need to be a looker, go back
When visual qualities are emphasized amorphous materials usually deliver them. Due to their low and even shrinkage straight and dimensionally accurate parts are easier to process. They also have a visually pleasing surface finish that can, if needed, look shiny.
Please bear in mind the limitations of amorphous plastics, however. They are prone to chemicals, fatigue, and stress-cracking. You will notice that these limitations are mentioned under every listed material.
Visual parts are often used for covering the inside of a device and its technical functions.
When you have gone through the selection criteria, you may reconsider the use of amorphous plastics. The best compromise between visual and technical qualities is introduced in the Technical path.
Examples of applications
Mobile phone covers
Mobile phone covers and housings are made of PC or PC/ABS. They deliver dimensional accuracy, high-quality appearance, good impact strength, and relatively high modulus. Their chemical resistance is not very good, however, and considering that they are subjected to sun-lotion, oil, grease, nail polish remover, urea, chili, etc., it is actually quite surprising that they survive the lifetime of a phone, up to seven years. They must have been designed with stress-cracking in mind: in a way, that continuous stress does not occur.
Mobile devices tend to heat up in active use. ABS is probably avoided for this reason.
Lego uses huge amounts of ABS in the production of its famous building blocks. They need to be dimensionally accurate, straight and tough, which could hardly be achieved with any lower-cost material. The transparent components are made of PC.
PS is a common choice in cheap toys which unfortunately very often results in brittleness and a short lifespan.
Lego must have a sophisticated quality-system as they manage to keep the grip between the blocks similar despite the difference in size and shape or production year and site.
Lego has invested heavily in order to replace the normal oil-based plastic grades with more sustainable plastics that should “offer the same safety, quality, durability and play experiences as our current materials.” (www.lego.com). One can only hope that such a challenge can be met.
TV remote controller
The housings of TV remote controllers are typically PC/ABS. The combination of improved impact resistance (PC) and chemical resistance (ABS).
You might have noticed that the snap lock on the battery lid is often broken, which easily happens if any continuous stress is subjected on the element.
WiFi router housings
What do you need from your product?
Impact resistance is always a good property, even if your product is mainly visual. A Wi-Fi box might fall off the shelf. From this perspective, PC, ABS, PC/ABS, and PPO are all materials with a good or excellent impact strength. PS and SAN are very brittle. HI-PS is a better choice.
If your product is well designed and properly molded with a proper tool, its visual quality should not differ much whether it is made of ABS, PC or ABS/PC. They all should come out straight and glossy.
ABS is the easiest to mold. Its tendency to warp is low. Burrs are minimal. Surface gloss is excellent and has a “drier” feel than that of PC .
PC requires a higher molding temperature and is a little more challenging to produce. For a professional manufacturer, this should not be an issue.
PS can be used for making a visually appealing product as well. The rattling echo of the components, however, does not increase the perceived quality.
Surfaces can be textured, glossy or satin-like matte. Small and appealing details can be etched or lasered on the mold cavity.
The surface finish of the backside of the component is often forgotten. Remember to specify it when going through the details of the tooling.
Long term exposure to direct sunlight affects the strength and color of plastic products. Even if your product is not mechanically stressed, you don’t want it to turn for example from white to yellow.
ASA is commonly known to resist UV light better than ABS, and it is used on side mirror housings of cars without any special coating to protect it from UV light. There is, however, typically a black rim around such components. This way it is difficult to notice the slight change in color when compared to the painted parts. You can not take as given, that any chosen ASA grade would be equally resistant. Talk to your material supplier and try to find a corresponding reference case.
The UV resistance of PS is poor.
Practically all amorphous materials can be painted with UV-protective paint or lacquer.
When designing a visually demanding product you have to take into consideration the UV-light effect on the color of the product, also in indoor use. Both the sunlight that penetrates the window and many indoor lights emit UV rays. It is common to see light-switches, printer lids or smoke alarms that have turned from pure white to nicotine yellow.
Improtant: The use of UV stabilized material is not enough, the colorants must be UV-stabilized as well.
Performance in high or low temperature
When visual qualities are emphasized in the material selection process, the product is not likely to be used in very hot or cold conditions. If your product is always used and stored indoors, service temperature is not a relevant factor.
In some cases, visual housings are used with kitchen appliances or electrical devices that generate heat. If temperatures higher than 70°C are likely, ABS or PS are not the best choices. PC and PPO tolerate high temperatures much better, even above 100°C.
Amorphous materials are avoided in medical applications because they are constantly handled with strong cleaning substances. Oily hands might also cause deterioration if the contact is repeating.
Chemicals and continuous load are an especially bad combination for amorphous plastics.
“Excellent chemical resistance” is often listed as an advantage for ABS. This is true when compared to PC, PPO or PS which are chemically very sensitive. However, acetone, for example, is fatal for ABS.
If your product is likely to be subjected to chemicals it is best to research and test it thoroughly. To be sure, see what the Technical path has to offer.
Which of the following best describes your product?
- Purely visual
- Go back
Do you consider visual appearance (e.g. high-gloss surface or straight edges) the most important factor for your component? Then choose Purely visual.
Or is the component only, or also, demanding in terms of mechanical performance or service conditions? If so, choose Technical.
In many cases neither of the above is crucial, and the cost of the material is a more important factor. Then follow the Commodity path.
You need high strength or modulus.
- Let's not mix things, go back
Adding reinforcement, typically 15-40 % (in some cases even up to 60%) of fiberglass, to plastic can significantly improve the strength, thermal resistance, and stiffness of your product. It also improves chemical resistance but not necessarily impact resistance.
Reinforced parts are usually functional components of heavy-duty products and made of semi-crystalline plastics like PA6, PA66, PBT, pPA, PPA or PEEK.
Amorphous plastics with reinforcements are sometimes used in boxes that require, in addition to impact resistance, extremely high strength.
The most common reinforcement by far is glass fiber. Carbon fiber is an attractive filler, but considerably costlier than glass and therefore usually used in high-end applications only.
The properties of the reinforced material are dependent on the base/matrix plastic:
- When dry, the modulus of reinforced PA6 and PA66 is on the same level as PBT while their strength is a little higher. When subjected to moisture, their mechanical properties can be reduced by up to 40%.
- The mechanical properties of PP+GF (with normal short fibers) reach approximately 70% of those of PBT.
- High-performance plastics like PEEK+GF and PPA+GF have better mechanical qualities than PBT+GF but are still within the same performance range. Their advantage is the ability to retain those qualities in considerably higher temperatures.
- The effect of temperature is especially important to take into consideration. In most cases, you can note the difference in component stiffness between room temperature and 80°C.
- High fiber content subjects the runner system and the cavity to abrasive wear. You need a properly hardened mold to cope with this.
- High fiber content dominates the process. When the tooling is done, your possibilities to improve the outcome with process parameters are small.
Examples of applications
Power tool housings
Power tool housings must transfer the torque from the engine to drill/screw. Today even battery-driven devices are so powerful, that it requires a lot of effort to hold the tool still. Some tools also have a hammer-action that requires impact fatigue resistance from the construction.
If you find old tools from the ’80s or ’90s, you may notice that using PC or PC+GF in the housings was quite common. In the construction site, tools may be subjected to paint, turpentine, glue or oil. This requires chemical resistance. It is also good to notice, that the screw bosses always cause continuous stress of some level. Semi-crystalline plastic is a safer choice.
Commonly used plastic in power tool housings is PA66+30GF, often with 2K TPE-S soft grip.
In smaller and less powerful hobby applications PC might still be used.
Garden and construction tools require high strength, ductility, and stiffness.
Lower cost tools may be made of PP+GF. The outcome is not as stiff as it would be with PA+GF, this naturally depends on the geometry of the product. If the handles bend, some of the working energy is lost, which makes the tool less efficient.
Impact modified PA6+30GF is quite typical material in tool handles. It does absorb some moisture. If you compare an indoor stored and outdoor stored tool, you may notice a difference in their bending resistance.
The use of long-fiber materials, both PP and PA, is increasing in branded high-quality tools. They do not significantly increase the stiffness of the product, but strength, impact strength (especially in cold conditions) and fatigue resistance are considerably improved.
Under the hood -applications
Reinforced semi-crystalline engineering plastics offer good strength, heat resistance, and chemical resistance.
PA66+GF is a common choice in under the hood -applications. Sometimes its performance is not sufficient in challenging thermal or chemical conditions. In such cases, high-performance plastics such as PPA+GF and PPS+GF are used instead.
PBT+GF is a valid engineering plastic with relatively similar properties to PA+GF. However, in the automobile industry, PA+GF is preferred in applications that are subjected to heat, trembling, and oil. In cars, PBT+GF used in electrical connectors, lighting, and interior components.
PP+GF (with long or short fibers) is widely used in the automotive industry, but its thermal properties are not sufficient near the engine.
What do you need from your product?
Strength and modulus
Very commonly used glass content with engineering plastics is 30%. Compared to unfilled plastics the product becomes considerably stiffer and stronger yet is still relatively easy to process.
Please see below the mechanical properties of PBT with different glass contents. The values are extracts from material datasheets and should be considered as theoretical. In practice, service conditions, fiber orientation, and weld lines may reduce them considerably.
- Yield stress 60 MPa
- Tensile modulus 2,7 GPA
- Strain at yield 8%
- Stress at break 120MPa
- Tensile modulus 7,5 GPa
- Strain at break 2,7 %
- Stress at break 145 MPa
- Tensile modulus 12 GPa
- Strain at break 2,3%
An increase of 10% in the fiber content, can improve strength and modulus by 20-35%. It is good to bear in mind, that the same can easily be achieved by modifying the geometry of the component. When the height of a bent element is increased slightly (for example from 10 mm to 11 mm) its stiffness may be improved correspondingly.
It is not rare to use 40% or even 50% glass content in demanding applications. Engineering plastics with up to 60% glass content are available, but not commonly used due to processing difficulties.
If cost is not an issue, carbon fibers lead to higher strength and modulus. In comparison:
PBT+40%CF (CELSTRAN PBT-CF40-09)
- Stress at break 175MPa
- Tensile modulus 14,5 GPA
There is also an increasing number of LGF (long glass fiber) materials available (mostly PA and PP). Compared to short fibers, long fibers increase material strength but their main advantage is improved impact resistance. The effect on modulus is minimal.
The highest modulus value found in the Campusplastics.com database is provided by Celstran PPS-CF50-02 AF3002 Natural, PPS with 50% long carbon fiber content. Its tensile modulus is above 40 GPa and Stress at break 155 MPa.
Good impact resistance
Reinforcing plastic increases its strength and modulus. Due to the increase in modulus, however, the material toughness is decreased which might lead to lower impact resistance. In some cases, on the other hand, fibers prevent cracks from propagating. To improve impact resistance, you need high glass content. Adding for example 15% of glass probably just makes the product more sensitive against impacts.
It is useful to perform practical tests with samples.
Polyamide is a common choice when both strength and stiffness are needed together with good impact resistance. For example, the injection-molded shaft of an ax is commonly made of PA6 +30-40% GF. Other reinforced semi-crystalline engineering materials (PBT, POM) are also reasonably impact-resistant. PPS is an exception and very brittle. When high-temperature performance is needed, PPA or PEEK is a much better choice than PPS.
Unfilled Polycarbonate is very impact-resistant. It is usually filled to increase strength and stiffness. Reinforcing may decrease its notch-sensitivity and therefore also makes it more impact resistant in some cases.
Carbon fiber is more expensive than glass fiber and makes the product stronger and stiffer, but more fragile.
Long-fiber (LF) materials increase impact resistance significantly. Long fibers are used mainly with PP and PA.
Note that low temperature affects impact resistance: Your product might be impact resistant in room temperature, but at -20°C it may turn brittle. This is especially the case with PP. Long fibers help in retaining impact resistance in low temperatures.
An impact-modified grade is available for most materials.
Does the function of your component require exceptionally high strength or stiffness?
What level of strength and stiffness do you expect from your component? Will it be subjected to forces that might lead to breakage or malfunction through bending? Does it need to be strengthened or made stiffer? Are you considering plastic as metal replacement?
Does the component need to be transparent?
If transparency is a nice option or a potential future modification please consider it carefully. Using transparent materials limits your options considerably and may affect the quality of the product.
You have chosen rubbery and elastic plastics.
- No soft plastics, thanks, go back
Thermoplastic elastomers (TPEs), is a family of six soft materials/material groups: TPE-S, TPE-V, TPE-O, TPE-U, TPE-E, TPE-A. Their advantage is their ability to return to their original shape after being stretched or elongated.
Silicone is a particularly heat-resistant option. It is not a thermoplastic and the manufacturing process of silicone products differs from injection molding.
Examples of applications
Soft handles (2K molding)
Power tools, pliers, toothbrushes, knives, etc. often have a rubbery area in their handle for a better grip.
The most commonly used TPE in 2K applications is TPE-S.
If your product is subjected to oils or heat (kitchen), TPE-V might be a good choice because of its improved thermal and chemical resistance.
TPE-U is sometimes used as well.
Proper adhesion/ponding to the first shot is a relevant factor in the selection of the right TPE. Your material supplier can help with this. Ask for a reference case with a similar service environment and mechanical requirements.
TPE-U has high friction and excellent wear resistance. It is the preferred material in roller wheels and industrial belting.
TPE-E and TPE-A are used on skiing boots. They are mechanically strong and perform well at low temperatures.
TPE-E is used on snowshoes for the same reason.
Car bumpers are today made of TPE-O. The same goes for airbag lids in the dashboard.
What do you need from your product?
When selecting a soft material, hardness and strain-at-rupture are probably more relevant than the modulus or the strength of the material.
Please note the difference between yield strength and tensile strength. If a component is stretched beyond its yield strength it will not return to its original shape.
When extreme flexibility is needed, your choices are limited.
At its softest TPE-S is like a flexible gel. For normal applications, its flexibility is usually adequate.
TPE-V is available relatively soft as well, from app. Shore-A 45.
Soft PVC is available from Shore-A 40.
Some material suppliers may offer products below these values.
Here is a useful comparison between different Shore values.
Improved impact resistance is one of the main reasons why components are made of soft materials.
TPE-U is known for its good impact resistance.
TPE-O is used in car bumpers.
Soft PVC is used in traffic cones and boat fenders.
Note that when operating in a cold environment, plastic components tend to become harder, stronger and stiffer but also lose some of their toughness and turn more brittle. This affects their impact resistance, so the lower end of the service temperature should be taken into consideration. In general, TPE-E and TPE-A serve well in cold conditions.
Resistance against continuous load
All plastic materials, including the rubbery, are prone to creep. If you stretch a plastic component for a prolonged period of time, it will not return to its original length.
The softer the material, the more sensitive it is to creeping.
TPE-O can not be recommended for purposes that require prolonged elongation.
Performance in elevated temperature
The rubbery material with the best thermal resistance is silicone with a service temperature of over 200°C. TPE materials used in injection molding have lower service temperatures.
TPE-S can usually not used in conditions above 100°C. TPE-O is slightly more tolerant.
TPE-A has the best thermal resistance of all TPEs, above 130°C.
The service temperature of each material may vary considerably depending on their hardness.
Note that at the upper end of the service temperature range, the material properties differ significantly from what they are at room temperature.
Please remember also that in plastic product design, continuous and temporary service temperatures are two different things.
Performance in low temperature
None of the TPE materials are especially prone to low temperatures. Their service temperature area starts from roughly -50°C which does not mean that their properties remain unchanged at that level. This is easy to test in practice using reference samples made of each material.
LD-PE is used in freezer box lids. Its Tg is -110°C.
Almost all plastics are available with UV stabilization. Prefer those when designing outdoor products.
TPE-S (SEBS), when stabilized, is known for its good UV resistance. It is important not to confuse SEBS and SBS. The UV resistance of SBS is poor.
Aliphatic TPE-U grades offer good color stability.
Dark colors are better than light ones because they prevent UV rays from penetrating deeper into the material.
Each TPE type has its strengths and weaknesses when in contact with organic solvents, acids, greases, bases, or other substances.
Sometimes, in chemically harsh conditions, silicone is the best option.
Temperature, duration of the exposure and mechanical load are important factors in chemical resistance. The lower they are, the better.
It is always good to test the chemical compatibility in practice by subjecting a sample of the material to the relevant chemicals. The test can be catalyzed by subjecting the sample to different stress conditions and/or by elevating the temperature.
Does the function of your component require elasticity, flexibility or rubberiness?
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Welcome to the Plasticprop material selection guide!
Choosing the right material is the key decision in plastic product design. A well-considered choice early in the process saves you a lot of unnecessary work and backtracking later on and the outcome has a better chance to be functional and durable.
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Plasticprop Essentials sample set
Easy way to explore and compare different plastics hands on: the Plasticprop Essentials sample kit.
The Plasticprop collection of plastic samples was set off by my daily need to assess and compare different plastics in practise. The Plasticprop Essentials contains 20 plastic samples with different characteristics. The set covers a wide range of materials that are commonly used in consumer goods, packaging, kitchen utensils, sporting equipment, vehicles and electronics. A few samples of high-performance and TPE grades are also included.
– Markus Paloheimo, Plastic Product Designer
Price 295€, vat 0%
"A properly designed plastic product is cost-effective but even more importantly, functional and long-lasting. Designing sustainable products requires theoretical understanding and practical experience. Please share your expertise and join the conversation. Let's design better plastic products together!"