Nylon Grades: Cast vs. Extruded, Filled Grade Guide
Nylon stock is not a single material — it spans two polymer chemistries (Nylon 6 and Nylon 6/6), two production methods (cast and extruded), and multiple fill systems (MoS₂, oil, glass fiber) that each change the performance profile substantially. Selecting the right grade before cutting stock is critical: using unfilled nylon where a dry-running bushing needs MoS₂-filled, or ordering extruded stock when a 6" diameter gear blank requires cast, will cause premature failure or machining problems.
TL;DR
- Cast Nylon 6: large cross-sections (up to 12" rod, 4" plate), low residual stress, slightly higher crystallinity — the default for gears, sheaves, and heavy bushings
- Extruded Nylon 6/6: tighter tolerances, smaller stock, slightly higher melt point — correct for bar-feed CNC, small rods, and thin sheet
- Nylatron GS (MoS₂-filled): the standard dry-running bearing grade; 5–10× better wear life than unfilled
- Nyloil (oil-filled): lowest friction of any nylon grade; FDA-compliant with food-grade oil; best for oscillating or intermittent motion
- Glass-filled (GS-30): doubles stiffness; NOT food-safe; abrasive to mating parts
- Unfilled natural: toughest, most impact-resistant; FDA-compliant; correct baseline where no specific performance gap exists
Nylon 6 vs. Nylon 6/6 — Polymer Chemistry
Both are polyamides but differ in monomer and properties:
In practice the production method matters more than chemistry. Nylon 6/6's higher HDT (185°F vs. 150°F at 264 psi) gives it a modest edge in applications near 200°F service temperature.
Cast Nylon 6
How It's Made
Cast nylon is produced by polymerizing caprolactam monomer in a temperature-controlled mold. The liquid monomer is poured directly into molds shaped to the finished stock geometry (rod billets, plate, tube). Polymerization occurs in the mold at atmospheric pressure, resulting in near-zero residual stress in the finished material.
Advantages
- Largest available cross-sections: rod to 12" diameter; plate to 4" thick × 24" × 96"; tube from 1" to 12"+ OD
- Lowest residual stress: no pressure-induced orientation — parts machine with minimal springback or stress relief cracking
- Higher crystallinity: modestly better stiffness and creep resistance vs. extruded Nylon 6/6 at comparable cross-sections
- Filled grade options: Nylatron GS, NSM, and Nyloil are all cast Nylon 6 variants
- Consistent through-section: no skin/core property variation typical of extruded rod
Limitations
- Length: cast rod and tube come in shorter billets vs. extruded bar stock; 24"–48" sections are typical
- Tolerance: cast sheet has slightly looser thickness tolerances than extruded; expect ±5–10% on thickness vs. ±3–5% extruded
- Availability: fewer distributors stock full cast range vs. extruded; lead times can be longer for large sizes
Extruded Nylon 6/6
How It's Made
Nylon 6/6 pellets are melted and forced through a die under pressure, then cooled in a water bath. The result is a bar or sheet with a denser, harder skin and a slightly different crystalline structure through the section.
Advantages
- Tight length tolerances: standard tolerance on rod diameter is ±0.010"–0.015" for sizes under 2"; better than cast for bar-feed CNC operations
- Long bar lengths: standard 6' and 12' bars for continuous bar-feed work
- Sheet thickness control: extruded sheet is produced to tighter thickness tolerances than cast plate
- Nylon 6/6 chemistry: slight edge in heat deflection and continuous service temperature
Limitations
- Size cap: practical maximum for extruded nylon rod in standard stock is 4" diameter; beyond that, use cast
- Residual stress: pressure during extrusion creates orientation stress — deep cuts on thick sections can cause part distortion
- No large-format plate: heavy plate (>2" thick) in standard stock is rare for extruded nylon; cast is the source for heavy plate
Filled Nylon Grades
Nylatron GS — MoS₂-Filled Cast Nylon 6
Nylatron GS is the industry-standard dry-running bearing grade. Molybdenum disulfide powder (2–3% by weight) is incorporated into the cast Nylon 6 matrix during polymerization. MoS₂ particles act as a solid lubricant at grain-boundary and surface-contact levels.
Performance vs. unfilled nylon (dry service):
- Coefficient of friction: 0.12–0.18 vs. 0.20–0.35 unfilled
- Wear life (bushing test): 5–10× longer than natural Nylon 6
- PV limit: 8,000–10,000 psi·ft/min vs. 3,000 unfilled
Identification: Black color. Standard color differentiates it from natural Nylon 6 on a parts tray — important in food environments where it must be kept out.
When to specify: Any dry-running or infrequently lubricated bushing, gear, or cam follower. The default choice when someone says "nylon bearing."
When NOT to specify: Food contact (MoS₂ is not FDA-approved for food contact). Electrical insulation (MoS₂ reduces resistivity).
Nylatron NSM / Nyloil — Oil-Filled Cast Nylon 6
Oil-filled nylon (trade names: Nyloil, Nylatron NSM depending on manufacturer and oil type) incorporates food-grade or mineral oil into the cast matrix. Under load and motion, oil migrates to the wear surface through the polymer network, providing continuous lubrication without an external supply.
Key properties:
- Lowest coefficient of friction of any unfilled or oil-filled nylon grade: 0.10–0.15 dry
- Very quiet operation — oil damping reduces vibration and noise transmission
- FDA-compliant when manufactured with FDA 21 CFR 178.3570 white mineral oil (confirm grade with supplier)
- Slightly lower tensile strength than unfilled: ~10,500 psi (oil acts as a plasticizer)
Best applications: Oscillating or reciprocating motion where start-stop cycles are frequent; food-zone bearings and cam followers; quiet-running textile and printing machinery components.
Identification: Natural/off-white or blue-green color depending on manufacturer.
Glass-Filled Nylon — GS-30 / Nylon GF33
Short E-glass fibers at 33% by weight roughly double nylon's flexural modulus and cut thermal expansion nearly in half. This is a structural grade, not a bearing grade.
Specify GS-30 for structural brackets, housings, or manifolds where deflection or creep is the failure mode. Critical trade-offs: glass fiber is abrasive to mating surfaces; the grade is notch-brittle (minimum 0.030" corner radius); it is not self-lubricating; it is not food-safe.
Grade Selection Matrix
Colors and Identification
| Color | Grade Indicator | Notes |
|---|---|---|
| Natural (off-white/cream) | Unfilled Nylon 6 or 6/6 | FDA-compliant; most common |
| Black | Nylatron GS (MoS₂) or carbon-loaded | MoS₂ = not FDA; carbon = better UV for outdoor |
| Blue | Nylatron NSM or manufacturer-specific | Metal-detector visible; FDA status depends on grade |
| Green | Certain proprietary cast Nylon 6 grades | Confirm FDA status with supplier |
Color-coding is not standardized across all manufacturers — always confirm grade designation by the full trade name or manufacturer spec sheet, not color alone.
Order nylon stock in the grade you need
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