POM vs. Nylon: A Comprehensive Engineering Comparison

In engineering plastics, people often compare POM and nylon, but the two materials are made for different performance needs. People choose POM (polyoxymethylene) because it has low friction, high stiffness, and great dimensional stability. This makes it a good choice for precision parts like gears, bearings, and bushings. Nylon (polyamide), on the other hand, is tough, can handle impacts, and is flexible. It is often used in parts that have to deal with changing loads or environments.

You shouldn’t just choose materials based on how strong they are or how much they cost. POM is best for situations where tight tolerances, low wear, and long-term dimensional accuracy are important. Nylon is better for situations where durability, impact resistance, and the ability to handle changes in moisture levels are important. Knowing these trade-offs helps make sure that the part works well for its entire service life.

What Are POM and Nylon? A Look at the Materials

Polyoxymethylene (POM) and Polyamide (Nylon) are both high-performance engineering plastics that are used in many different fields. Even though they are both thermoplastics, their structural properties, molecular arrangements, and how they react to stress are different, which makes them good for different uses.

Polyoxymethylene (POM) or Acetal

POM, which is also called acetal, is a very crystalline engineering plastic that is very stable in size, has low friction, and is very resistant to wear. Because POM has a crystalline structure, it is rigid and doesn’t absorb much moisture. This makes it a great choice for applications that need precision and mechanical properties that stay the same over time.

Some important features are:

• Low friction: Great for gears, bushings, and moving parts that don’t need to wear out quickly.

• POM is a great choice for precision parts because it doesn’t absorb moisture and stays stable in different environmental conditions.

• High stiffness and strength: This makes it useful for structural applications because it stays stable even in tough conditions.

• Not very good at withstanding impacts: The crystalline structure makes POM more brittle than other materials like Nylon, which is great for precision.

POM is often used in gears, bearings, and other precise mechanical parts where it is important that the parts fit together perfectly and last a long time.

Polyamide (PA6 / PA66) nylon

Polyamide, or nylon, is a thermoplastic that is either amorphous or semi-crystalline. It is known for being very tough, able to withstand impacts, and having a high elongation at break, which makes it good for parts that need to absorb energy without breaking or cracking. There are different types of nylon, such as PA6 (Polyamide 6) and PA66 (Polyamide 66), which are a little stronger and better at withstanding heat.

Some important features are:

• High toughness: This material can take a lot of stress without breaking, making it perfect for automotive parts and machinery.

• Nylon can absorb moisture, which can make it swell or shrink. This can change the size of the material and cause it to break down in places with a lot of moisture.

• Nylon is great at resisting fatigue because it can handle repeated stress cycles without breaking down. This makes it perfect for flexible uses.

• Less stiff: Nylon is more flexible than POM and doesn’t hold its shape as well over time, so it’s not as good for precision applications.

People often use nylon in things like industrial parts, textile machinery, car parts, and consumer goods where flexibility and resistance to damage are important.

Comparing how materials act

Material takeaway: POM’s crystalline structure makes it better for high-precision parts because it is more stable and resistant to wear. Nylon, on the other hand, is tougher and more resistant to impact, but it doesn’t work as well in different environments. Knowing these basic differences helps you choose the right material based on how well it works and how much exposure it gets to the environment.

Comparison of Mechanical Properties from a Quantitative Engineering Perspective

Engineers need to think about more than just the cost and basic tensile strength when choosing between POM and Nylon. The real performance of these materials depends on how they react to stress, impact, wear, and temperature. This part compares important mechanical properties, such as tensile strength, flexural modulus, impact resistance, wear resistance, and how well the material resists friction.

Strength and Modulus of Tension and Flexure

Tensile strength and flexural modulus are two important ways to measure how well a material holds up when it is bent or pulled. They help us guess how POM and Nylon will act when they are used to hold things up.

• Because of its crystalline structure, POM is usually stiffer and stronger in tensile and flexural tests. This is because it has high rigidity and low elongation.

• Naylon has a semi-crystalline or amorphous structure, which makes it less stiff but better at breaking and stretching. This means it can handle stress without breaking right away.

Mühendislik paket servisi: POM is better for applications that need a lot of stiffness and load-bearing, while Nylon is better for parts that need to be flexible and stretch, like those that are exposed to shock loading or stress often.

Strength and resistance to impact

Impact resistance tells you how much energy a material can take before it breaks.

• Naylon is very strong and can withstand impacts, especially when it’s cold, because it has a rubbery butadiene phase (in some grades). It doesn’t crack or break when it’s under a lot of stress.

• POM is strong and stiff, but its crystalline structure makes it more brittle when it is hit. It is likely to crack when it is under sudden stress, especially when it is cold.

The engineering takeaway is that Nylon is the best material for high-impact uses, especially those that need to be tough in changing conditions. POM, on the other hand, is better for applications that need stiff, precise parts that won’t be hit hard.

How well it resists wear and how it behaves with friction

Both POM and Nylon are very durable, but they behave very differently when they come into contact with other materials.

• POM has a low friction coefficient and is very resistant to wear when dry. People often use it for gears, bearings, and sliding parts because it cuts down on wear without needing lubrication.

• Naylon is still good at resisting wear, but it doesn’t work as well when there is dry friction. It takes in moisture, which can make it more durable, but it can also make it unstable in areas with a lot of moisture.

Mühendislik paket servisi: POM is better for applications where low friction and little wear are important, especially in dry places. Nylon is better for things like textile machinery or car parts where taking in moisture can make things work better.

In conclusion, when choosing between POM and Nylon, think about the application’s mechanical load, impact exposure, wear conditions, and environment. POM is better for precision, stiffness, and low friction, while Nylon is better for impact resistance and toughness, especially in applications that are flexible or changeable.

Performance in terms of heat and the environment

The thermal and environmental properties of materials are very important when deciding if they are right for a certain use. Both POM and Nylon are made for heavy industrial use, but they react very differently when they are exposed to heat, moisture, chemicals, or UV radiation. To choose the right material for your needs, you need to know these things.

Temperature for Heat Deflection and Temperature for Continuous Use

The Heat Deflection Temperature (HDT) test tells you how well a material can hold up under a certain load at high temperatures without changing shape. The HDT of POM is higher than that of Nylon, which makes it better for high-precision uses where parts are exposed to moderate temperatures. POM keeps its size better in hot places than Nylon, which tends to soften and lose strength when it gets hot.

• POM usually has a higher HDT than Nylon (some grades of Nylon are more heat-sensitive), which makes it good for gears, bearings, and other parts that are exposed to thermal stress in machines used in the automotive and industrial industries.

• Naylon, on the other hand, can’t be used in places where the temperature is too high for long periods of time.

The continuous use temperature is the temperature range in which the material can work well for long periods of time. POM is usually better for high-heat environments, while Nylon is better for moderate temperatures.

Absorption of moisture and stability of size

One big difference between how POM and Nylon keep their shape is how well they absorb moisture.

• POM doesn’t absorb much moisture, usually less than 0.2%. This means that its mechanical properties and dimensional accuracy stay the same even when the weather is humid or wet. Because of this, POM is a better choice for precision parts like gears and bearings that need very tight tolerances.

• Naylon absorbs more moisture because it is more hydrophilic. The amount of moisture it absorbs depends on the grade, but it is usually between 2% and 8%. This causes the material to swell in size, which can change its shape and make it more slippery when it gets wet. This is especially important for long-term or high-precision uses where dimensional stability is a must.

POM is great for applications where moisture resistance and dimensional stability are important. Nylon, on the other hand, works better in environments where moisture is present, like textile machinery or seals.

Resistant to chemicals, oil, and UV rays

• POM is very resistant to a wide range of chemicals, such as acids, alkalis, and fuels. It also works well in places where there is oil and solvent.

• Naylon is also resistant to many oils and fuels, but it doesn’t handle strong acids and bases as well as POM does. Nylon doesn’t hold up as well to oxidation and can break down when it comes into contact with strong chemicals.

• UV resistance: POM doesn’t do well in UV light, and it will break down faster if it is exposed to sunlight for a long time. Some grades, on the other hand, are UV-stabilized and can be used outside.

• Naylon can break down when exposed to UV light, but it can also be made with UV stabilizers and additives, which makes it a better choice for outdoor use where UV exposure is a concern. Stabilizers make Nylon last longer when it’s outside or in other places where it’s exposed.

POM usually works better than Nylon in harsh chemical environments, but Nylon works better in outdoor applications that are exposed to UV light.

Mühendislik paket servisi: POM is the best choice for thermal stability and dimensional control, especially in dry, high-temperature, and precise applications. But if the application involves being outside, in the sun, or in the rain, Nylon might be a better choice, as long as its ability to absorb moisture is taken into account in the design.

Material Science Insight: Why POM and Nylon Act So Differently

The way POM and Nylon behave differently is because of the way their molecules and polymers are made. POM is better at dimensional stability and wear resistance because of these structural features. Nylon is better at impact resistance and toughness. The following insights from material science look at the main differences that affect engineering results.

The Crystal Structure and Chain Structure of POM

POM (Polyoxymethylene) is a semi-crystalline polymer, which means that its polymer chains are arranged in an ordered way to make crystalline areas that are mixed with amorphous areas. POM’s high level of crystallinity gives it better stiffness, dimensional stability, and resistance to wear. The tightly packed molecular structure makes it harder for chains to move, which makes the material less likely to creep and more consistent under load.

Engineering consequence: POM keeps its shape and mechanical properties better over time because its crystalline structure is ordered. This makes it great for applications that need tight tolerances, like gears, bearings, and precision parts. But it also makes things more brittle, especially when they hit something, and you have to be very careful about the temperature while working with it to avoid problems like warping.

Nylon’s ability to form hydrogen bonds and absorb water

Polyamide, or nylon, is a type of polymer that is amorphous to semi-crystalline. It is made up of hydrogen bonds between polymer chains. This makes Nylon more hygroscopic, which means it can absorb moisture more easily than POM. When Nylon takes in water, the hydrogen bonds break, which makes the material grow and change its mechanical properties, such as swelling in size and increased friction.

Engineering consequence: Nylon becomes unstable in size when it absorbs moisture, especially if it does so over time. This makes it less useful for situations where consistent dimensions or high accuracy are needed, like in mechanical parts that fit tightly or parts that need to be exact in size. On the other hand, Nylon’s ability to absorb moisture makes it more resistant to impact and fatigue, which makes it better for things like seals and automotive parts that are exposed to different levels of humidity.

Effects of Long-Term Creep and Fatigue

Both POM and nylon show creep behavior over time, which means that they change shape when they are under a lot of stress for a long time. But because of their different structures, the mechanisms and effects of creep are very different.

• POM doesn’t creep much because its crystalline structure keeps its shape well under pressure. This makes POM a great choice for uses that need long-term accuracy, like precision gears and bearings.

• Naylon is better at absorbing stress and stopping cracks from spreading because it has a more flexible, amorphous structure. But Nylon is more likely to creep when it is under constant stress, especially when it is hot or in a stressful environment.

Engineering consequence: POM is the best choice for applications that need to be very stiff and not change shape over time. Nylon is better for parts that move or are exposed to vibration, impacts, or changing stresses because it is tougher and more resistant to fatigue.

Material Science takeaway: The basic differences in how POM and Nylon work are due to the differences in polymer crystallinity and hydrogen bonding. POM’s crystalline structure makes it stable in size and resistant to wear, while Nylon’s ability to absorb moisture makes it tough and resistant to impact but makes it harder to keep its size stable. Engineers can choose the right material for the job by knowing these differences and how they will affect the environment.

CNC Machining and Injection Molding: How Well They Work in Manufacturing

When deciding between POM and Nylon for CNC machining or injection molding, the way the material is processed has a big impact on how efficient, high-quality, and cost-effective it is. Both materials have their own advantages, but they behave differently during manufacturing processes like chip formation, flow behavior, and shrinkage, which can affect the whole production process.

How CNC Machining Works

When it comes to CNC machining, POM and Nylon act differently. POM is usually easier to machine because it has a crystalline structure.

• Chip formation: When machining POM, it makes clean, well-formed chips, which makes it great for making high-precision parts like gears, bushings, and cams. POM can handle high cutting speeds without getting too hot or smearing because of its crystalline structure. Because nylon is amorphous, it tends to make softer chips, which can cause heat to build up, especially when machining at high speeds. It can also cause some gumming or material to stick to the tool, which means you have to change and adjust the tool more often.

• Surface finish: POM usually gives a smoother surface finish because it has a low coefficient of friction and doesn’t stick to chips very well. It can make smooth finishes that are good for sliding parts and precision parts. Because nylon tends to make a surface that is a little rougher than POM, it often needs more finishing after machining to get the same surface quality, especially in high-precision applications.

• Tolerance stability: POM is the best choice for tight tolerances over long periods of time because it doesn’t creep or absorb moisture very well. Nylon can change size when it gets wet or after being machined because it absorbs more moisture. This could affect the stability of long-term tolerances.

Things to Think About When Injection Molding

For making a lot of parts, injection molding is often the best way to do it. POM and Nylon can have very different flow properties and processing needs.

• Flow behavior: POM flows very well, which makes it easy to fill complicated molds and thin-walled features. It works best for high-precision molding jobs that need smooth surfaces and a consistent thickness, like gears and bearings. Because nylon has a higher molecular weight, it flows a little slower than POM, especially when molding things with a lot of precision. But it is more flexible and durable, which makes it great for use in large parts that need to be strong and resistant to impact.

• Shrinkage: POM shrinks very little and in a predictable way when it cools, which means that molding results are always the same and dimensions are always accurate. This is why POM is great for uses where part accuracy and consistency are very important. Nylon shrinks more than POM, which can make mold design more sensitive and require careful temperature control during the cooling process to avoid warping or dimensional instability.

• Warping and mold design sensitivity: Nylon absorbs moisture during the molding process because it is hygroscopic. This makes it warp or change shape as it dries. Because it absorbs moisture, Nylon is also more sensitive to mold design parameters like the locati0n of the gate and the rate at which it cools. POM is less likely to warp because it doesn’t absorb moisture well and its shrinkage rates are stable. However, to keep parts consistent, mold temperature and injection speed must be carefully controlled.

For CNC machining, POM is usually better than Nylon because it makes better chips, has a better surface finish, and stays the same size. POM is often the best choice for injection molding parts that need to be very precise because it doesn’t shrink much and flows well. Nylon, on the other hand, may be better for parts that need to be impact-resistant and can handle more moisture and shrinkage. To get the best performance out of both materials in manufacturing settings, you need to carefully think about the processing parameters.

Cost and Lifecycle Factors

When comparing the costs of POM and nylon, the total cost should include more than just the cost of the materials. The lifecycle costs of each material are different because of how well they work, how they need to be processed, and the conditions they will be used in. When choosing materials, engineers and procurement managers need to think about how long they will last, how well they will resist wear and tear, and how easy they will be to maintain.

Cost of Materials vs. Cost of Processing

• Cost of Materials: Nylon is usually cheaper than POM, which makes it a good choice for projects that don’t need to be very expensive. Nylon’s lower initial cost can be very helpful when making a lot of something. POM, on the other hand, is usually more expensive per kilogram because it has better mechanical properties and dimensional stability. However, it might be the better choice for high-performance applications.

• Cost of Processing: POM is often easier to machine and molds well with less scrap, which lowers the cost of processing high-precision parts. Nylon is easier to mold in large amounts, but it can cost more to process because it absorbs moisture, which means more drying steps before molding, and it may need more tool adjustments because it shrinks more.

How long it lasts, how often it wears out, and how often it needs to be replaced

• POM: Parts made of POM tend to last longer because they have low friction, are resistant to wear, and keep their shape. This is especially true for precision mechanical parts. This means that parts that are always moving or carrying a load, like gears, bushings, and bearings, need to be replaced less often.

• Nylon: Nylon is stronger and more resistant to impact, but it usually wears out faster in places with a lot of friction and stress. If nylon parts are exposed to dry conditions where moisture can’t get in or isn’t present, they may need to be replaced more often.

Total Cost of Ownership (TCO)

The total cost of ownership includes the cost of materials, processing, and long-term performance, which includes maintenance and replacement.

• POM has higher initial costs, but because it lasts longer, needs less maintenance, and has less downtime because it is more durable, it has a lower TCO in precision applications.

• Naylon costs less at first, but in high-load or high-wear situations, it often has a higher total cost of ownership (TCO) because it wears out faster and needs to be replaced more often.

Cost takeaway: POM is usually more cost-effective over its whole life cycle, even though it costs more up front. This is because it is more precise, resistant to wear, and long-lasting. Nylon is a good choice for low-cost applications where toughness and impact resistance are important, but its higher wear and moisture sensitivity can make it more expensive to own in tough conditions.

When to Use POM or Nylon in Common Situations

POM and Nylon are both useful engineering plastics, but their different properties make them better for certain uses. Designers and manufacturers can pick the best material for their needs, the environment, and the way they make things if they know where each material works best.

Uses for POM

Polyoxymethylene (POM) is a common material for precision mechanical applications that need tight tolerances and long-lasting durability. It has low friction, high dimensional stability, and great wear resistance.

Some common uses for POM are:

• Because it doesn’t wear down or create friction, gears POM is often used to make gears. It is often used in precision gears for things like cars, industrial machines, and robots.

• Bushings POM bushings are great for high-performance machines that need low-friction parts without lubrication because they don’t wear out easily and stay the same size.

• POM is great for sliders, cams, clamps, and clips because it is very stiff and doesn’t creep, which keeps its dimensions accurate over time.

Thanks to POM’s ability to keep dimensions accurate in moving applications and places where friction or wear would otherwise hurt performance, these parts work better.

Uses for Nylon

People know that nylon (polyamide) is tough, can withstand impacts, and can absorb shock and energy. It works well in situations where parts are exposed to changing loads, bending, or moisture.

Some common uses for nylon are:

• Bearings made of nylon are often used in cars, factories, and consumer goods because they are strong and can handle being hit. They also last a long time, especially when they are lubricated with moisture that has been absorbed.

• Housings made of nylon are common in electrical and electronic parts that need to be able to withstand impact and look good. It can help improve dimensional stability in some situations, like in automotive or industrial enclosures, because it can absorb moisture.

• Impact-loaded structural parts Nylon is a common material for parts in cars and machines that need to be able to handle a lot of stress and be flexible, like bumpers, structural reinforcements, and suspension parts. Nylon is a great choice for flexible, high-stress applications because it can handle dynamic loading without breaking or failing.

Choosing the Right Application

• When you need load-bearing parts like gears, bushings, and precision mechanical parts that are precise, have low friction, and are resistant to wear, use POM.

• Kullanım nylon for parts that need to be tough and flexible, like bearings, housings, and dynamic parts that are exposed to moisture.

When choosing between POM and Nylon, it’s not just about strength. You also need to know if the part needs to be stable and wear-resistant under load (POM) or tough and impact-resistant under changing conditions (Nylon).

Standards and Testing References in the Industry

When choosing materials like POM and Nylon, following industry standards and testing references makes sure that the material meets requirements for performance, safety, and durability. ASTM and ISO standards give engineers and procurement managers clear ways to test and set performance goals, which helps them make smart, compliant choices for their applications.

Standards for Wear and Mechanical Parts (ASTM / ISO)

ASTM and ISO standards that cover mechanical properties, wear resistance, and overall performance are used to test both POM and Nylon.

• ASTM D638 (Tensile Properties of Plastics) This standard looks at the tensile strength and modulus of materials so that engineers can see how POM and Nylon will react when they are pulled or stretched.

• ASTM D790 (Flexural Properties of Plastics) This standard tests the strength and flexural modulus of plastics. It helps compare POM and Nylon in situations where bending stresses are present, like in structural components.

• ISO 9001 (Quality Management Systems) This quality standard is often used by manufacturers to test plastic parts under certain conditions to make sure they meet certain standards for quality and mechanical performance.

• ISO 2137 (Wear and Friction Testing) This standard lays out ways to test how well materials resist wear and how much friction they have. This is especially important for things like gears and bushings that slide against each other.

Methods for Testing Moisture and the Environment

Both POM and Nylon have to pass tests that mimic real-world conditions to see how they react to moisture and other environmental factors.

• ASTM D570 (Water Absorption of Plastics) This test checks how much moisture materials can absorb. It sets a standard for how Nylon behaves when it absorbs moisture and how it affects its size over time.

• ISO 62 (Determination of Water Absorption) This test measures how much water a plastic material can soak up in a controlled environment. This helps engineers figure out how Nylon will change shape and whether it will work well in humid or wet places.

• ASTM D256 (Izod Impact Test) This test checks how well Nylon can handle impacts, which is useful for comparing its toughness to POM, especially in situations where there are sudden shocks or impact forces.

The takeaway for the industry is that using ASTM and ISO standards for mechanical, wear, and environmental testing makes sure that POM and Nylon materials meet the necessary standards for safety, durability, and long-term performance. Manufacturers can confidently choose materials that meet both performance and compliance standards when they follow these rules.

How to Choose Between POM and Nylon for Engineers and Buyers

When deciding between POM (Polyoxymethylene) and Nylon (Polyamide), you need to carefully look at how each material works, how it affects the environment, and how it can be made. The choice should be based on the specific needs of the application, taking into account cost-effectiveness, wear resistance, precision, and long-lasting performance.

The following guide to choosing materials will help engineers and buyers make decisions based on the most important factors that affect performance and cost.

Step 1: Figure out how precise you need it to be

• High precision, tight tolerances, and dimensional stability → POM POM is great at keeping its dimensions accurate over time, which makes it perfect for high-precision uses like gears, bearings, and mechanical parts.

• Moderate precision, flexibility, and toughness → Naylon Nylon is better for parts that need to be tough and flexible, like those that need to be able to withstand impacts.

Step 2: Look at the weather and the surroundings

• Naylon can absorb moisture, which helps it stay tough and strong in humid or changing environments. But in some cases, the part’s performance may be affected by the moisture absorption, so it’s important to think about whether this will happen.

• POM is good for dry places or situations where moisture exposure is low because it doesn’t absorb moisture and stays stable and resistant to wear.

Step 3: Resistance to shock and impact load

• Naylon is great for parts that need to be able to handle a lot of stress, like car parts or structural parts, because it is very tough and can absorb a lot of energy.

• Low to moderate impact load and wear resistance: POM POM works well in precise, low-impact applications like gears, where wear resistance is more important than flexibility.

Step 4: Think about the cost and the way the product is made.

• Injection molding, high-volume production → Naylon Nylon’s ability to flow well makes it a good choice for large-scale injection molding with complicated shapes. It also tends to be less expensive than POM, which can help lower production costs when a lot of the same thing is made.

• CNC machining, precision parts → POM POM’s machining properties, like making clean chips and giving better surface finishes, make it perfect for low-volume, precision parts where tolerance stability is very important.

Selection Matrix in Action

Checklist for Buyer-Engineer Alignment

• Is it important to have dimensional stability? → POM

• Does the part need to be able to handle moisture or humidity? → Naylon

• Is it important for the application to be impact-resistant? → Naylon

• Are you making a lot of complicated parts? → Naylon

• Does the part need to be very precise or able to withstand a lot of wear? → POM

Final Decision Insight: Choosing between POM and Nylon depends on a number of factors, including accuracy, the environment, mechanical loads, and the way the parts are made. For parts that need to be very precise and resistant to wear in dry, stable environments, POM is the best choice. For parts that need to be dynamic and able to handle high impacts in environments that are exposed to moisture, Nylon is better.

Summary — Important Engineering Lessons

POM is best for applications that need high accuracy and low friction, like gears, bearings, and other moving parts where dimensional stability and wear resistance are important. Nylon, on the other hand, is better for parts that need to be tough and resistant to impact, especially in environments where the load changes or moves.

When deciding between POM and Nylon, you should think about how the materials will be used, how they will be exposed to the environment, and how they will be made, not just how strong they are. Taking all of these things into account together will lead to better performance and more efficient production over the part’s service life.

SSS

Is POM better than nylon for making gears?
Yes. POM is the best material for precision gears and bearings because it has low friction, high wear resistance, and stable dimensions. Nylon’s higher friction and sensitivity to wear make it less suitable for gear applications that need to last a long time.

How does moisture change the size of Nylon?
Nylon’s size can change a lot when it absorbs moisture. Nylon is hygroscopic, which means it absorbs moisture and swells. Nylon 6 is usually more affected than Nylon 66. This makes it less useful for applications that need very tight tolerances.

Which material works better for machines, POM or Nylon?
POM machines are better for making precise parts. It makes clean chips, keeps the surface quality, and stays within tight tolerances. When machining nylon, it is softer and more likely to get hot and have surface problems.

Is POM more costly than nylon?
Yes. Because it is more dimensionally stable and resistant to wear, POM usually costs more. For parts that don’t need to be very precise and need to be impact-resistant, nylon is a better choice.

Can Nylon be used instead of POM in parts that need to be very precise?
No, usually not. POM is more reliable over time than nylon when it comes to precision mechanical parts because nylon doesn’t hold its shape or resist wear as well.