Nylon Properties: Mechanical, Thermal & Chemical
Nylon plastic (polyamide, PA) properties span a wide range depending on grade, production method, and moisture content. Unfilled Nylon 6 and 6/6 deliver tensile strengths around 12,000 psi, a continuous-use rating of 200°F, and a self-lubricating surface that tolerates dry running against steel. The critical variable that separates nylon from every other common engineering thermoplastic is moisture absorption — it reaches 2–9% by weight at saturation, shifting dimensions, stiffness, and impact resistance in ways that must be accounted for at the design stage.
TL;DR
- Tensile strength: ~12,000 psi (dry); drops ~15–20% at moisture saturation
- Continuous use temperature: 200°F (93°C); short-term to 300°F
- Moisture absorption: 1.5–3.5% at 24 hours; up to 9% at saturation — the single biggest design variable
- Coefficient of friction vs. steel (dry): 0.20–0.35 unfilled; lower with MoS₂ or oil-filled grades
- Electrically semi-insulating; dielectric properties degrade with moisture uptake
- Chemical resistance: excellent vs. hydrocarbons and bases; avoid strong acids, phenols, and ketones
Mechanical Properties
Tensile, Compressive, and Flexural Strength
The drop in flexural modulus from dry to conditioned state — roughly 40–50% — is the most consequential moisture effect on structural applications. A nylon beam or bracket designed to dry-state stiffness will deflect significantly more in service if it equilibrates to ambient humidity.
Impact Resistance
Nylon is notch-sensitive in its dry state. Absorbed moisture reduces notch sensitivity and increases impact toughness:
This behavior is opposite to most thermoplastics: nylon actually becomes tougher and less brittle as moisture content rises. Parts expected to survive impact loads in wet or humid environments benefit from conditioning before installation.
Hardness and Wear
PV limit (pressure × velocity) is the combined load/speed threshold above which the bearing surface overheats. Exceeding it causes surface melting and rapid failure. Nylatron GS and Nyloil significantly extend the dry PV limit of nylon in bearing applications.
Thermal Properties
Temperature Limits
The higher melt point of Nylon 6/6 gives it a modest advantage at elevated temperatures. For sustained duty above 200°F, neither grade is suitable without consulting deflection data at operating temperature. Consider PEEK for continuous service to 480°F.
Thermal Expansion and Conductivity
The CTE of unfilled nylon is roughly twice that of steel. In assemblies where nylon mates with steel over a wide temperature range, clearance must account for differential expansion — this is compounded by the moisture-driven dimensional change discussed below.
Moisture Absorption — Critical Property
Nylon's polyamide backbone contains amide groups (–CO–NH–) that form hydrogen bonds with water molecules. This is not surface absorption — water penetrates throughout the bulk of the material, with rate and final content driven by relative humidity, temperature, and cross-section thickness.
Absorption Rates and Final Content
Property Changes with Moisture
| Property | Dry (0.2% moisture) | 50% RH (2.5–3%) | Immersed (8–9%) |
|---|---|---|---|
| Tensile Strength | 12,000 psi | ~10,000 psi | ~9,000 psi |
| Flexural Modulus | 500,000 psi | 300,000 psi | 150,000–200,000 psi |
| Izod Notched Impact | 0.9 ft-lb/in | 2.0 ft-lb/in | 3.0+ ft-lb/in |
| Hardness (Shore D) | 80 | 72–75 | 65–70 |
| Linear Dimension | baseline | +0.5–0.8% | +1.5–2.0% |
Design guidance: For any part where a bore or shaft clearance tolerance is tighter than 0.005"–0.010" per inch of diameter, specify Delrin (moisture absorption <0.25%) or dimension the nylon part at its expected service moisture content. See the Acetal vs. Nylon comparison for a full design-decision matrix.
Chemical Resistance
Resistant
- Hydrocarbons (oils, fuels, greases): excellent
- Dilute alkalis: good
- Alcohols: good
- Dilute organic acids (acetic acid <10%): fair to good
- Salt solutions, seawater: good
Not Resistant
- Strong mineral acids (HCl, H₂SO₄): poor — attack amide bonds
- Concentrated acetic acid, formic acid: attack and swell
- Phenols, cresols: attack the polymer matrix
- Ketones (acetone, MEK) at elevated concentrations: fair to poor
- Oxidizing acids: poor
- Water at elevated temperatures (>180°F continuous): hydrolytic degradation
Nylon performs well in petroleum-based fluid environments — hydraulic oil, gear oil, diesel fuel. It is commonly used for fuel system and hydraulic components. However, avoid contact with brake fluid (glycol-based), which can attack nylon over time.
For aggressive chemical environments, compare against UHMW polyethylene (broad chemical resistance, low friction) or PEEK (near-universal chemical resistance at elevated temperatures).
Electrical Properties
Nylon is a semi-insulating thermoplastic. Its electrical properties are suitable for low-frequency insulation duty but degrade substantially with absorbed moisture.
For electrical insulation in humid or wet environments, nylon is a poor choice. Acetal (moisture absorption <0.25%) maintains its electrical properties far better. For demanding electrical applications, consider glass-filled grades (which reduce moisture uptake in the filled zones) or switch to a low-absorption material entirely.
Effect of Filled Grades on Properties
Glass-filled grades offer the best dimensional stability and stiffness but sacrifice toughness and food compliance. MoS₂-filled grades are the standard dry-running bearing grade. Oil-filled grades are the quietest and most self-lubricating, with FDA compliance where oil is food-grade.
Comparing Nylon Properties Against Peer Materials
For engineers cross-shopping materials, the key differentiators versus nylon's main competitors:
- Delrin: nearly identical strength and hardness, but <0.25% moisture absorption, better dimensional stability, and lower coefficient of friction than unfilled nylon — at similar cost
- UHMW: lower tensile strength (~6,000 psi) but far superior abrasion resistance (6× nylon) and moisture immunity; better for liner and chute applications
- PEEK: 2–3× tensile strength of nylon, 480°F continuous service, but 10–15× the cost per pound
- Cotton Phenolic: better bearing performance in flooded-oil service; nylon wins in dry-running and impact resistance
The nylon comparisons page has side-by-side tables for each of these materials.
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