7 Properties of Nylon: Everything you Need to Know

You see it every day, but you probably don’t recognize it. It’s the small, white gear inside a printer, silently enduring thousands of cycles. It’s the bristles on a toothbrush, the fabric of a durable backpack, and the lifesaving material in a car’s airbag. It’s nylon, one of the most versatile and misunderstood workhorses in the entire world of engineering polymers.

My name is Clive, and for the better part of 25 years, I’ve been designing parts out of plastic. I learned early on that calling a material “plastic” is like calling every animal a “creature.” It’s technically true, but utterly useless. The difference between a cheap toy made of polystyrene and a high-performance engine component made of nylon is as vast as the difference between a jellyfish and a racehorse.

I’ll never forget my first real lesson on nylon’s deceptive nature. We were designing a set of precision snap-fit clips for a medical device. In our dry, air-conditioned lab in Arizona, the prototypes worked flawlessly. The clips, made from a standard grade of Nylon 6, had the perfect balance of stiffness and flexibility. They clicked into place with a satisfying, high-quality snap. We were heroes. We shipped the first batch of 10,000 units to a new assembly plant in Florida.

Three weeks later, the phone rang. It was the plant manager. “These clips don’t work,” he said, his voice flat and angry. “They’re soft. They bend, they don’t snap, and half of them are out of tolerance.”

We were baffled. We checked our designs, our mold data, our material certificates. Everything was perfect. It wasn’t until an old toolmaker on the factory floor asked a simple question that the lightbulb went on. “What’s the humidity down there?” he grunted. Florida’s humidity was hovering around 85%. Our lab in Arizona was a bone-dry 15%. In the three weeks it took to ship them, the nylon clips had been quietly drinking water from the humid air, swelling up, and losing their stiffness. That single, overlooked property—nylon’s love for water—cost the company over $50,000 and taught me a lesson I’ve never forgotten: with nylon, you’re not just designing with a plastic; you’re designing with a sponge.

Before we dive into the technical details and put the two major types of nylon in a head-to-head showdown, here is a quick summary of the seven key properties that define this incredible material.

Quick Reference: The 7 Core Properties of Nylon

Why is Nylon Considered a High-Performance Engineering Polymer?

When engineers talk about “plastics,” we mentally divide them into two camps: commodity plastics and engineering plastics. Commodity plastics are the cheap, disposable materials of everyday life—polyethylene in your milk jugs, polypropylene in your yogurt cups. Engineering plastics, like nylon, are a class apart. They are chosen specifically for their mechanical and thermal properties to replace traditional materials like metal.

High Tensile Strength

The first pillar of nylon’s performance is its exceptional tensile strength. This is a measure of how much pulling force a material can withstand before it stretches and breaks. The magic behind this strength lies in its molecular structure. Nylon is a polyamide, meaning its long polymer chains are linked together by powerful amide bonds. Even more importantly, these chains are further attracted to each other by hydrogen bonds—the same force that holds water molecules together.

Think of it like microscopic Velcro. Each individual polymer chain is a long strand, but the hydrogen bonds between the chains act as countless tiny hooks, gripping adjacent chains with incredible force. When you try to pull the material apart, you’re not just stretching the chains; you’re fighting to unhook this massive network of intermolecular Velcro. This is why a thin nylon rope can have a higher tensile strength than a steel cable of the same weight. It’s this property that makes nylon the go-to material for high-stress applications like automotive timing belts, industrial conveyor belts, and load-bearing brackets.

Exceptional Toughness and Impact Resistance

Strength alone isn’t enough. Glass is incredibly strong under tension, but it’s brittle. If you hit it with a hammer, it shatters. Nylon, on the other hand, is not just strong; it’s tough. Toughness is a material’s ability to absorb energy and deform without fracturing. It’s the difference between a material that snaps and one that bends.

Nylon’s toughness comes from the semi-crystalline nature of its structure. Under a powerful microscope, you’d see that nylon is made of two distinct regions: highly ordered, tightly packed crystalline regions and disorganized, spaghetti-like amorphous regions.

• The Crystalline Regions are like the bones of the material. They are rigid, tightly packed, and provide the core strength and stiffness.
• The Amorphous Regions are like the connective tissue. They are flexible and allow the polymer chains to move and untangle under stress, absorbing the energy of an impact.

When a nylon part is struck, the amorphous regions absorb the initial shock, while the strong crystalline regions prevent the material from breaking. This combination makes nylon phenomenally resistant to impact and fatigue, which is why it’s used for things like power tool housings, skateboard wheels, and protective gear. It can take a beating day after day and just bounce back.

What Makes Nylon So Resistant to Wear and Abrasion?

One of nylon’s most prized characteristics is its low coefficient of friction and high abrasion resistance. In simple terms, it’s naturally slippery and doesn’t wear out easily when rubbed against other surfaces, particularly metal. This is why, for decades, one of the most common applications for nylon has been in unlubricated gears and bearings.

Imagine a small gear in a vending machine. It might cycle hundreds of times a day, rubbing against a metal shaft. If that gear were made of a softer plastic, it would quickly wear down, leaving a fine plastic dust and eventually failing. If it were made of metal rubbing against metal, it would require constant grease or oil to prevent it from seizing up.

Nylon solves both problems. Its smooth, long-chain polymer structure allows surfaces to glide past each other with minimal resistance. This self-lubricating property is so effective that nylon parts can often run for millions of cycles with no external lubrication at all. This makes it a miracle material for clean environments (like food processing) or inaccessible locations (like inside a sealed motor) where adding grease is impossible or undesirable.

Furthermore, its inherent toughness means that even when it does wear, it does so very slowly. It resists being scratched or gouged, a property known as abrasion resistance. This is why it’s used for everything from conveyor belt guide rails to the wear pads on heavy construction equipment.

How Does Nylon Handle High Temperatures and Chemicals?

The final pieces of nylon’s performance puzzle are its resistance to heat and chemicals, which solidify its place as a true metal replacement.

Thermal Stability

The same strong hydrogen bonds that give nylon its tensile strength also give it a high melting point. It takes a significant amount of thermal energy to break those bonds and allow the polymer chains to melt and flow. Standard grades of nylon can typically operate continuously at temperatures around 80-95°C (175-200°F), with high-temperature, glass-filled grades pushing that well over 150°C (300°F).

This allows nylon to survive in hostile environments like a car’s engine bay. It’s used for radiator end tanks, engine covers, and intake manifolds, where it has to withstand constant heat from the engine without softening or deforming.

Chemical Resistance

Nylon’s tightly packed, semi-crystalline structure also makes it difficult for many chemicals to penetrate and attack the polymer chains. It is exceptionally resistant to:

• Oils, Greases, and Fuels: This makes it a staple in the automotive industry for fuel lines, oil pans, and power steering fluid reservoirs.
• Alcohols and Common Solvents: It won’t degrade when exposed to cleaning agents or industrial solvents.

However, it’s not invincible. Nylon is susceptible to attack from strong acids and bases (like sulfuric acid or sodium hydroxide) and certain chlorinated solvents. But for the vast majority of industrial applications, its chemical resistance is more than sufficient.

We’ve now seen the incredible strengths of this material. But as my story from Florida illustrates, nylon has a dark secret—an Achilles’ heel that can turn this high-performance champion into a soft, swollen failure. In the next section, we will confront this critical weakness head-on and put the two most common types of nylon—Nylon 6 and Nylon 6,6—in a head-to-head showdown to see which one manages this weakness best.

This absorbed water acts as a plasticizer. It lubricates the polymer chains, allowing them to slide past each other more easily. The consequences are catastrophic for a precision part:

1. Dimensional Instability: The part literally swells up as it absorbs water. A part that was perfectly in tolerance in a dry climate can become oversized and unusable in a humid one.
2. Loss of Stiffness (Modulus): The plasticizing effect makes the material softer and more flexible. My “snappy” clips became soft and gummy.
3. Reduced Strength: The tensile strength of the material can drop by 30% or more when it’s fully saturated with water.

This single property is the number one reason well-designed nylon parts fail in the real world. But not all nylons are created equal in their thirst for water. This brings us to the main event: the two most common members of the polyamide family, Nylon 6 and Nylon 6,6. They look and feel nearly identical, but a tiny difference in their molecular blueprint creates a world of difference in their performance.

What is the Difference Between Nylon 6 and Nylon 6,6?

To the naked eye, a gear made of Nylon 6 and one made of Nylon 6,6 are indistinguishable. The difference lies in their chemical backbone. Both are polyamides, built from repeating molecular units containing carbon atoms and amide groups. The numbers—6 and 6,6—simply refer to the number of carbon atoms in the monomers, or chemical building blocks, used to create the polymer chain.

• Nylon 6 is made from a single type of monomer called caprolactam, which contains 6 carbon atoms. Think of it as building a long chain using only one type of Lego brick, over and over again.
• Nylon 6,6 is made from two different monomers: hexamethylenediamine (which has 6 carbon atoms) and adipic acid (which also has 6 carbon atoms). Think of this as building a chain by alternating between two different types of Lego bricks.

This might seem like a trivial distinction, but it fundamentally changes the way the polymer chains pack together. The alternating structure of Nylon 6,6 allows its chains to align into a more tightly packed, uniform, and highly ordered crystalline structure. There are fewer gaps and disorganized regions. Nylon 6, being made of a single monomer, forms a slightly less dense and less ordered structure.

Imagine stacking firewood. A pile of perfectly uniform, straight logs (Nylon 6,6) will pack together much more tightly and rigidly than a pile of logs that are all slightly different or bent (Nylon 6). This tighter molecular packing is the key to Nylon 6,6’s superior performance in almost every category.

Which Nylon is Better for My Application?

Choosing between these two materials is a classic engineering trade-off between performance and cost. Nylon 6,6 is the higher-performance material, but Nylon 6 is cheaper and easier to manufacture into parts. Let’s put them in a head-to-head showdown.

My Florida clip disaster was a textbook case for choosing Nylon 6,6. The application required tight tolerances and consistent mechanical “snap” action. By choosing the cheaper Nylon 6, we saved a few cents per part but created a product that was functionally useless in the intended environment. The slightly lower moisture absorption of Nylon 6,6 would have kept the clips within their functional tolerance range. It was a classic case of being penny-wise and pound-foolish.

How Do Additives Like Glass Fiber Change Nylon’s Properties?

So far, we’ve only talked about “unfilled” nylon. But in the world of high-performance engineering, raw nylon is often just the starting point. The real magic happens when you start adding reinforcements to it, much like adding steel rebar to concrete. The most common reinforcement by far is glass fiber.

You’ll see this specified on a drawing as “Nylon 6,6, 30% GF,” meaning it’s a blend of 70% nylon resin and 30% short, chopped glass fibers by weight. These fibers are mixed in with the molten plastic before it’s injection molded. The result is a composite material that is far more capable than the sum of its parts.

The “Rebar in Concrete” Effect

Imagine the base nylon polymer as concrete. It’s strong in compression but can be flexible and prone to creep. The short glass fibers act like microscopic rebar, creating an internal skeleton within the plastic part. This skeleton provides three massive benefits:

1. Massively Increased Strength and Stiffness: Adding 30% glass fiber can easily double or triple the stiffness (flexural modulus) and tensile strength of the nylon. The composite material is far more rigid and can handle much higher loads without bending.
2. Dramatically Improved Dimensional Stability: This is the secret weapon against nylon’s water-loving nature. The rigid glass skeleton physically prevents the nylon from swelling as much when it absorbs moisture. A 30% GF nylon part might only swell half as much as an unfilled part under the same humid conditions. If my Florida clips had been made of glass-filled nylon, the problem would likely never have occurred.
3. Higher Heat Resistance: The glass fibers help the part retain its shape and stiffness at much higher temperatures. This is measured by the “Heat Deflection Temperature” (HDT), which is the temperature at which a material starts to deform under a specific load. Glass-filled nylons have a much higher HDT, making them essential for components that sit near hot engines or motors.

Of course, there are trade-offs. Glass-filled nylons are more brittle (less impact resistant), more abrasive on the molds used to make them, and don’t produce the same beautiful glossy finish as unfilled nylon. But for structural parts, the benefits are undeniable.

We now have a deep understanding of the material itself—its strengths, its critical weakness, and how to combat that weakness with material selection (Nylon 6,6) and reinforcement (glass fiber). But even with the perfect material, a poorly designed part will still fail. How do you design snap-fit clips that don’t break, gears that don’t strip, and enclosures that don’t warp?

I was a young engineer, proud of a complex housing I’d designed for an industrial sensor. It was to be molded from a high-grade, 30% glass-filled Nylon 6,6. It had mounting tabs, a snap-fit lid, and a series of deep ribs for stiffness. On the CAD screen, it was a masterpiece of efficiency. In reality, it was a disaster. The first parts out of the mold were horribly warped, with ugly sink marks opposite the ribs, and the mounting tabs—which had sharp, 90-degree inside corners—were cracking off if you looked at them sideways.

The senior molding technician, a man named Gus who had forgotten more about plastic than I would ever know, walked over with one of the cracked parts. He didn’t say a word. He just pointed to the sharp corner where the tab met the body of the housing. Then he pointed to the deep sink marks on the otherwise cosmetic surface. Finally, he held the warped part up and rocked it on the flat granite inspection table. It wobbled like a bent dinner plate. “Plastic,” he said, finally looking at me, “hates two things more than anything else in the world: sharp corners and big, fat lumps of material. You gave it both.”

That expensive lesson taught me that understanding the material is only half the battle. The other half is understanding the rules of the process—in this case, injection molding. A part must be designed not just for its final function, but for the violent, high-pressure, high-temperature journey it takes from a plastic pellet to a solid object.

What are the 5 Golden Rules for Designing Nylon Parts?

Based on that failure and countless projects since, I’ve distilled the art of designing with nylon down to five non-negotiable commandments. Following these rules won’t just make your parts stronger; it will make them cheaper, more consistent, and far less likely to end up in the scrap bin.

Rule 1: Thou Shalt Not Have Sharp Internal Corners

This is the first and most important commandment of plastic part design, and Gus’s lesson to me. A sharp internal corner is a stress concentrator. When a part is put under load, the stress “flows” through it like water through a pipe. A sharp corner forces that flow to make an abrupt turn, causing the stress to pile up right at the corner, reaching levels many times higher than the average stress in the part. Nylon, for all its toughness, is “notch sensitive.” This means that a tiny crack or a sharp corner gives the forces a perfect place to start a fracture.

• The Fix: Always add a generous radius to all inside corners. The rule of thumb is that the inside radius should be at least 0.5 times the wall thickness. For example, for a part with a 3mm wall, the minimum inside radius should be 1.5mm.
• Why It Matters: The radius acts like a smooth, curved elbow in a pipe, allowing the stress to flow evenly without concentrating in one spot. This single feature dramatically increases the strength and impact resistance of the part. For my cracked sensor housing tabs, adding a proper radius would have distributed the load and prevented the fractures entirely. This is the cheapest insurance policy you can buy in plastic design.

Rule 2: Thou Shalt Maintain Uniform Wall Thickness

This was the second half of Gus’s lesson. Plastic shrinks as it cools in the mold. If a part has a thick section next to a thin section, the thick section will cool much more slowly and shrink for a longer time. This differential shrinkage creates massive internal stresses. The thick section pulls on the thin section as it cools, causing the part to warp—just like my sensor housing.

Furthermore, the outside of a thick section will solidify while the inside is still molten. As the molten core finally cools and shrinks, it pulls the semi-solid outer surfaces inward, creating a depression on the surface called a sink mark. This is why my “beautiful” housing had ugly divots opposite every single one of my thick, chunky ribs.

• The Fix: Design the part with a wall thickness that is as uniform as possible throughout. If you need to add ribs for stiffness, they should be no more than 50-60% of the thickness of the wall they are attached to. This prevents them from becoming “big, fat lumps of material” that cause sink and warp.
• Why It Matters: Uniform walls lead to uniform cooling, uniform shrinkage, and minimal internal stress. This results in dimensionally stable, flat parts without cosmetic defects. It’s the key to high-quality injection molding for any plastic, but especially for semi-crystalline materials like nylon that have relatively high shrinkage rates.

Rule 3: Thou Shalt Design for Moisture Expansion

As we established in the previous section, this is nylon’s unique superpower and its greatest curse. A designer who ignores moisture absorption is designing for failure. You simply cannot hold a +/- 0.05mm tolerance on a large nylon part that will be used in an uncontrolled environment. The dimensional change due to humidity will be far greater than your entire tolerance band.

• The Fix: First, consult the material datasheet. It will explicitly state the expected dimensional change from a “dry-as-molded” state to a “50% relative humidity (RH)” and a “fully saturated” state. You must account for this growth in your design. For critical interfaces, like a bearing bore or a press-fit pin, perform a tolerance analysis that includes this moisture-induced expansion. If the stability is absolutely critical, choose Nylon 6,6 over Nylon 6, and strongly consider a glass-filled grade to reduce the swelling.
• Why It Matters: This prevents field failures. It ensures that assemblies that fit together perfectly in a climate-controlled factory will still fit together after sitting in a shipping container in the tropics. It’s the difference between a reliable product and one that generates constant customer complaints. My Florida snap-fit clips were a direct violation of this rule.

Rule 4: Thou Shalt Respect Fiber Orientation in GF Grades

This rule applies specifically to glass-filled (GF) nylon. When molten GF nylon is injected into a mold, the suspended glass fibers tend to align themselves in the direction of the plastic’s flow, like logs floating down a river. This means the final part is anisotropic—it has different properties in different directions. The part will be incredibly strong and stiff in the direction of fiber alignment but significantly weaker and more brittle perpendicular to that alignment.

• The Fix: A good designer works with the mold maker to predict the flow of plastic and, therefore, the fiber orientation. Critical features like snap-fits or mounting tabs should be oriented so that the stress is applied parallel to the expected fiber direction. Avoid designing features where the load path forces stress to pull the fibers apart from each other.
• Why It Matters: Failing to account for anisotropy can lead to parts that are strong in one direction but inexplicably crack and fail when loaded in another. It’s a subtle but critical effect. A cantilever snap-fit beam, for example, should be filled from its base towards its tip, ensuring the fibers run along its length, giving it maximum bending strength.

Rule 5: Thou Shalt Design Smart Snaps and Hinges

Nylon is famous for its use in snap-fit connectors and living hinges due to its excellent flexibility and fatigue resistance. But these features must be designed correctly to survive repeated use.

• The Fix: For snap-fits, use well-established design principles for cantilever beams, ensuring the strain at the base of the beam does not exceed the material’s limit (typically around 2-5% for unfilled nylon). Taper the beam’s thickness to distribute the stress evenly. For living hinges, a very thin, radiused section (around 0.25-0.40mm thick for unfilled nylon) allows for repeated flexing without failure.
• Why It Matters: A properly designed snap-fit will function reliably for thousands of cycles. A poorly designed one, with high stress concentration at its base (violating Rule #1), will break off after only a few uses. Correct design leverages nylon’s inherent properties to create elegant, low-cost assembly features.

How Can I Ensure My Nylon Parts Succeed?

Success with nylon comes from a holistic approach. It begins with acknowledging its seven core properties—strength, toughness, wear resistance, chemical resistance, heat resistance, low friction, and its critical hygroscopic nature. It continues by making an informed choice between Nylon 6 and 6,6, and deciding if the added performance of glass fiber is necessary. Finally, and most importantly, it requires embedding these five design commandments into your process. Design with radii, maintain uniform walls, account for moisture, respect fiber flow, and use proven guidelines for flexible features. By marrying deep material knowledge with disciplined design, you can unlock the full potential of this incredible polymer and create parts that are not just functional, but truly robust.

Conclusion

Nylon is far more than just a generic plastic; it’s a family of high-performance engineering polyamides with a remarkable combination of properties. Its inherent strength and toughness make it a substitute for metal in gears and bearings, while its low friction and high wear resistance ensure those parts last. Its ability to withstand heat and chemicals allows it to survive under the hood of a car, an environment that would destroy lesser materials.

However, we learned that its greatest strength is shadowed by a critical weakness: its hygroscopic nature. Nylon’s tendency to absorb water from the air can cause it to swell and lose stiffness, a lesson I learned the hard way. This weakness forces a critical choice between the more stable, heat-resistant (but more expensive) Nylon 6,6 and the easier-to-process Nylon 6. To truly combat this instability and boost performance, we saw how the addition of glass fibers acts like rebar in concrete, creating a stronger, stiffer, and more dimensionally stable composite.

But even the most advanced material is doomed to fail if the part itself is poorly designed. The five golden rules of nylon design—avoiding sharp corners, maintaining uniform walls, accounting for moisture, respecting fiber orientation, and designing smart flexible features—are not mere suggestions. They are the fundamental principles that separate reliable, cost-effective parts from a pile of warped, cracked, and useless scrap. By understanding the material’s soul and respecting the rules of the manufacturing process, you can transform simple nylon pellets into the robust, high-performance components that make our modern world work.

Frequently Asked Questions (FAQs)

1. Is nylon safe for food contact?
It depends on the specific grade. Many manufacturers offer special FDA-compliant or EU-approved grades of nylon (both PA6 and PA66) that are formulated with additives considered safe for food contact. You must always specify this requirement and request certification from the material supplier.

2. Why does nylon sometimes turn yellow over time?
Nylon is susceptible to degradation from ultraviolet (UV) radiation from sunlight. This UV exposure breaks down the polymer chains, leading to discoloration (yellowing or browning) and making the material more brittle. For outdoor applications, it is essential to use a UV-stabilized grade or, more commonly, a black-colored nylon that uses carbon black as a UV inhibitor.

3. Can you 3D print with nylon?
Yes, nylon is a very popular material for advanced Fused Filament Fabrication (FFF) 3D printing, especially for creating functional prototypes and end-use parts. However, it is notoriously difficult to print. Due to its high moisture absorption, the filament must be kept perfectly dry in a heated dry box. It also has a high shrinkage rate, which requires a heated build plate and a fully enclosed, heated build chamber to prevent warping and layer splitting.

4. How do you properly dry nylon pellets or 3D printing filament?
Nylon must be dried before processing (molding or printing). The standard method is to use a desiccant dryer, which circulates hot, dry air through the material for several hours. For 3D printing filament, a dedicated filament dryer is best. You can also use a convection oven set to a low temperature (typically 70-80°C or 160-175°F) for 4-6 hours, but never use an oven that is also used for food.

5. Is nylon recyclable?
Yes, nylon is a thermoplastic, meaning it can be melted and reformed. It typically falls under the recycling symbol #7 (“Other”). However, its recycling is not as common or widespread as plastics like PET (#1) or HDPE (#2). Recycling facilities that can handle nylon are less common, and separating different types (Nylon 6 vs. 6,6) and filled vs. unfilled grades can be challenging.

References

• DuPont. (n.d.). Zytel® PA Polyamide Resin Design Guide. Retrieved from https://www.dupont.com/content/dam/dupont/amer/us/en/transportation-industrial/public/documents/dupont-zytel-pa-design-guide.pdf
• BASF. (n.d.). Ultramid® (PA, PPA) Product Brochure. Retrieved from https://plastics-rubber.basf.com/global/en/performance_polymers/products/ultramid.html
• SpecialChem. (2022). All About Polyamide (PA)/Nylon Plastic: Properties, Grades & Applications. Retrieved from https://omnexus.specialchem.com/selection-guide/polyamide-pa-nylon-plastic
• Protolabs. (n.d.). Designing with Nylon. Retrieved from https://www.protolabs.com/resources/design-tips/designing-with-nylon/

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