Nylon FAQ: 10 Common Questions Answered

Nylon (polyamide, PA) is one of the most versatile engineering thermoplastics in the market, offering high strength, excellent fatigue resistance, good chemical resistance, and a broad range of filled grades for specific performance applications. It is available as extruded rod, sheet, and tube, as well as large-format cast billets and custom profiles. This FAQ addresses the most common questions buyers and engineers ask when selecting and specifying nylon stock shapes.

What is the difference between cast and extruded nylon?

Cast nylon (usually nylon 6) is produced by an anionic polymerization process — liquid caprolactam monomer is poured into molds and polymerized in-place. Extruded nylon (nylon 6 or 6/6) is produced by melting pellets and extruding through a die. The key differences:

• Size capability: Cast nylon can be produced in very large shapes — billets, rods, and plates up to 40–50″ diameter or thickness — that would be impractical to extrude. This makes cast nylon the only practical option for large gear blanks, pulleys, and wear pads.
• Molecular weight: Cast nylon has a higher molecular weight, yielding better impact strength, better wear resistance, and superior fatigue resistance vs. extruded nylon 6.
• Porosity: Cast nylon is essentially void-free with very uniform microstructure; extruded nylon in large cross-sections can exhibit minor core porosity.
• Cost: Extruded nylon in standard sizes is typically less expensive and more widely stocked. Cast nylon in large shapes is cost-effective vs. machining from extruded rod.

For standard precision-machined parts in smaller cross-sections (under 4″ diameter), extruded nylon is usually the first choice. For large structural components or high-wear applications, cast nylon 6 excels. See the nylon grades guide for a full comparison.

What is the difference between nylon 6 and nylon 6/6?

Nylon 6 (polycaprolactam) and nylon 6/6 (polyhexamethylene adipamide) are the two dominant polyamide types in engineering stock shapes. Key differences:

• Melting point: Nylon 6/6 has a higher melting point (~500°F / 260°C vs. ~428°F / 220°C for nylon 6) and better short-term heat resistance.
• Moisture absorption: Both absorb moisture significantly (2.5–9% at equilibrium in water), but nylon 6/6 absorbs slightly less than nylon 6 in some conditions.
• Machinability: Nylon 6 is considered slightly more machinable and is preferred for large cast billets. Nylon 6/6 extrudes more cleanly and is common in smaller rod and sheet.
• Impact strength: Nylon 6 (especially cast) typically has higher impact strength.
• Cost: Nylon 6 extruded stock is generally slightly less expensive than nylon 6/6 equivalents.

In most structural and wear applications, either type is acceptable. Specify nylon 6/6 when the higher melting point or slightly lower moisture sensitivity is critical; specify nylon 6 (especially cast) when maximum impact strength or large-format shapes are needed. See the nylon 6 vs. nylon 6/6 comparison for more detail.

How does moisture absorption affect nylon performance?

Nylon is hygroscopic — it absorbs moisture from the environment, and this absorption significantly changes its properties:

• Dimensional change: A 1″-square nylon 6 part will grow approximately 0.003–0.006″ in a side when going from dry-as-molded to equilibrium moisture content at 50% relative humidity. This must be accounted for in tight-clearance fits.
• Property change: Moisture acts as a plasticizer — it reduces tensile strength and stiffness by 20–40%, while increasing elongation at break and impact strength. Machining dry nylon produces parts with higher as-machined stiffness; the parts then soften and grow as they equilibrate in service.
• Equilibration time: Large cross-section parts can take weeks to months to fully equilibrate in a humid environment.

For precision applications, condition nylon parts to the expected service humidity before final machining, or design with moisture-equilibrated dimensions in mind. Glass-filled and oil-filled grades absorb somewhat less moisture than unfilled. The nylon properties guide includes moisture absorption curves by grade and cross-section.

What filled nylon grades are available?

A broad range of filled nylon grades is available for specific performance needs:

• MoS₂-filled (Nylasint, Nylatron GS): Molybdenum disulfide filler reduces friction and improves bearing/bushing wear life. The standard go-to for dry-running bearing applications.
• Oil-filled (Nylatron NSM): Internally lubricated with oil released at the wear surface; excellent for low-speed, high-load bearing applications where external lubrication is impractical.
• Glass-filled (GF30): 30% glass fiber significantly increases stiffness (~3× unfilled flexural modulus), reduces moisture absorption, and improves creep resistance. Tradeoff is reduced impact strength and abrasive machining.
• Carbon-filled: Highest stiffness and lowest CLTE; black color. Used in structural brackets and thermally stable components.
• Glass + MoS₂: Combined filler for both stiffness and wear; used in high-load, low-speed gear and bearing applications.
• Heat-stabilized grades: For continuous service above 250°F (121°C).

See the complete nylon grades and filled variants guide for a property table comparing unfilled and filled options.

What are the best practices for machining nylon?

Nylon is very machinable but has several specific challenges:

• Moisture: Machine nylon in its as-received state (if equilibrated to your environment) rather than fully dry — dry nylon machines slightly differently and may swell after machining in a humid shop.
• Heat buildup: Nylon has a relatively low thermal conductivity — heat from machining stays in the chip and workpiece. Use sharp tooling, light feeds, and compressed air or mist coolant to prevent thermal damage.
• Dimensionality: For tight-tolerance holes, bore to final size rather than drilling and reaming — nylon's elasticity causes reamed holes to spring back.
• Surface finish: Nylon can leave a slightly fuzzy surface on fine finishes. Take light finishing cuts with sharp tooling.
• Speeds: 400–800 SFM for turning; higher speeds improve surface finish. Feeds around 0.002–0.005 in/rev.

Glass-filled grades are more abrasive — expect accelerated tooling wear and plan for more frequent insert changes. The nylon machining guide covers tooling geometry and fixturing in detail.

What sizes is nylon stocked in?

Nylon is one of the most extensively stocked engineering plastics:

• Rod: Extruded nylon 6 and 6/6 from 1/4″ to 6″+ diameter; cast nylon 6 from 1/2″ to 50″+ diameter in large-format billets
• Sheet/Plate: Extruded in 24×48 and 24×96 in. panels, 1/16″ to 4″ thick; cast sheet from 1/2″ to 6″+ thick
• Tube: Extruded in common OD/ID combinations; cast nylon custom tube available
• Profiles: Cast nylon gears, wear strips, flanges, and custom profiles available from cast nylon converters

Filled grades (MoS₂, glass, oil) are typically available in rod and sheet up to 6″ diameter/thick; sizes above that may require special casting. Check the nylon line card for current stock and minimum quantities.

Does nylon need to be annealed?

Annealing is recommended for cast nylon and extruded nylon in large cross-sections or when tight dimensional tolerances must be held after machining:

• Why anneal: Extruded nylon rod and cast billets contain residual stress from the manufacturing process. This stress is released during machining, causing parts to warp or change dimension after machining — sometimes hours or days later.
• Annealing procedure: Heat to 275–300°F (135–150°C) in an air oven for 1–4 hours (depending on cross-section), then cool slowly in the oven (1–2°F per minute). Quenching in water will re-introduce stress.
• When required: Parts with wall sections over 1/2″, precision bores or slots, parts that must hold ±0.001–0.002″ after machining, and parts that will see thermal cycling in service.

For most non-critical applications, annealing is not required. Discuss with your machinist whether annealing before rough-machining and then finishing after a relaxation period is appropriate.

Are there FDA-approved nylon grades for food contact?

Yes. Both nylon 6 and nylon 6/6 are available in FDA-compliant grades meeting 21 CFR 177.1500. These are used in food-processing equipment including slicing guides, conveyor wear strips, cutting boards, and packaging machinery. Cast nylon 6 (FDA) is particularly common in large wear components for meat and dairy processing. Natural (uncolored) nylon is the FDA-compliant grade; black nylon (carbon-black filled) is typically not food-contact rated. When ordering for food-processing applications, specify "FDA-compliant nylon" and request a letter of compliance. See the nylon FDA and food-grade guide for regulatory detail.

How does nylon cost compare to acetal?

Extruded nylon rod and sheet runs approximately $4–$10/lb, comparable to or slightly below acetal (Delrin) at $5–$12/lb. Cast nylon 6 in large billets is often more economical than equivalent extruded acetal on a per-volume basis for large shapes. Filled grades (glass, MoS₂) typically cost 20–40% more than unfilled equivalents. In total part-cost terms, nylon's slightly lower machinability compared to acetal (more tendency to fuzz, gum in certain cuts) can increase machine time for very tight tolerance work. For general engineering parts where either material would work, evaluate total part cost (material + machining yield) rather than raw material price per pound.

What lead times should I expect for nylon stock shapes?

Extruded nylon 6 and 6/6 in standard rod, sheet, and tube sizes are typically in stock at major distributors with same-day or next-day ship. MoS₂-filled nylon is widely stocked; glass-filled and oil-filled grades may require 1–2 weeks. Cast nylon 6 in standard billets (3–12″ diameter, 6–24″ length) is usually in stock or available in 1–2 weeks from cast nylon converters. Non-standard sizes, very large billets (over 24″ diameter), and specialty grades (heat-stabilized, custom compounded) may require 4–8 weeks or longer. Confirm availability at the time of order and request a lot cert with your shipment.

Can nylon be bonded or welded?

Nylon can be joined by hot-gas welding using a nylon welding rod, achieving 60–80% of parent material tensile strength — adequate for fabricated assemblies such as tanks, guards, and wear liners. Butt-fusion welding is used for pipe-grade nylon in fluid-handling systems. Nylon bonds poorly with most structural adhesives due to its low surface energy; chemical etching or flame treatment followed by urethane or epoxy adhesive can achieve moderate bond strength for non-structural applications. Ultrasonic welding and vibration welding are standard in injection-molded part assembly. Solvent cementing is not practical for nylon (it has no common solvents). For large wear components assembled to metal structures, mechanical fastening remains the most reliable method.

Is nylon suitable for outdoor applications?

Unfilled nylon is not recommended for long-term outdoor UV exposure without protection. UV radiation degrades the surface of nylon, causing yellowing, chalking, and eventual embrittlement. For outdoor applications, UV-stabilized nylon grades are available; alternatively, black nylon (carbon-black-filled) is inherently UV-stable and a good choice for outdoor structural wear components. Nylon also absorbs atmospheric moisture, which causes dimensional change and property shift in outdoor conditions — account for equilibrium moisture content in the design. For outdoor chemical resistance, nylon resists most dilute acids, alkalis, and organic solvents but is attacked by strong acids and oxidizing agents. If UV stability, minimal moisture absorption, and outdoor chemical resistance are all required, consider acetal (Delrin) as alternatives.

More related guides

Cross-cluster suggestions to help shoppers and engineers explore adjacent topics:

Applications

• Bushings Bearings
• Wear Strips Guide Rails
• Gears

Industries

• Food Beverage
• Automotive

Compare to other materials

• Acetal Vs. Nylon
• Nylon Vs. Uhmw
• Nylon Vs. Cotton Phenolic

Frequently asked questions — Nylon FAQ

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        "text": "Cast nylon (nylon 6) is polymerized in molds from liquid monomer, enabling very large shapes, higher molecular weight, better impact strength, and superior wear resistance. Extruded nylon is less expensive in standard sizes and widely stocked. For parts under 4 in. diameter, extruded is standard; for large structural or high-wear parts, cast nylon 6 is preferred."
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