The short answer
Unfilled general-purpose nylon 66 injection grades typically list 1.13–1.14 g/cm³ density, a 260–262°C / 500–504°F melting point and 70–85°C / 158–185°F heat deflection at 1.8 MPa. Data sheets show two columns, dry as molded and conditioned. Absorbed moisture cuts tensile modulus from about 2.8–3.6 GPa dry to about 1.1–1.6 GPa conditioned and raises notched impact. Choose lubricated, heat-stabilized or nucleated by the part. Toughened PA66 is a separate family.
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Paste it as written. A polymer chemist will tell you which grade it calls for, suggest equivalents and quote it by email.
This page covers unfilled, general-purpose nylon 66 for injection molding. For glass-reinforced grades see PA66 30% glass, and for supertough grades see impact-modified nylon. Full typical values are on nylon 66 properties, and the wider family is on the nylon page. Reference grades in this window include Zytel 101L (see Zytel 101L specs and equivalents), Ultramid A3K and Vydyne 21SPC. If you are deciding between PA6 and PA66, see nylon 6 vs. nylon 66.
Typical spec window
| Property | Typical range | Test method |
|---|---|---|
| Density | 1.13–1.14 g/cm³ / 0.0408–0.0412 lb/in³ | ISO 1183 or ASTM D792 |
| Viscosity | Viscosity number about 150 cm³/g on the standard injection grades checked; some sheets add MVR (100–120 cm³/10 min at 275°C / 527°F, 5 kg) | ISO 307, 96% sulfuric acid; MVR by ISO 1133 |
| Yield stress, dry / conditioned | 81–95 MPa / 11,700–13,800 psi dry; 50–66 MPa / 7,300–9,600 psi conditioned | ISO 527 |
| Tensile modulus, dry / conditioned | 2.8–3.6 GPa / 406,000–522,000 psi dry; 1.1–1.6 GPa / 160,000–232,000 psi conditioned | ISO 527 |
| Notched Charpy, 23°C / 73°F | 5–6.6 kJ/m² dry; 12–20 kJ/m² conditioned | ISO 179/1eA |
| Heat deflection, dry | 70–85°C / 158–185°F at 1.8 MPa; 190–220°C / 374–428°F at 0.45 MPa | ISO 75-1/-2 |
| Melting point | 260–262°C / 500–504°F | ISO 11357 (DSC) |
| Water absorption | About 1.1–1.3% in 24 h immersion; 2.3–3.1% at equilibrium in 23°C / 50% RH; 8–9% saturated in water | ISO 62 |
| Mold shrinkage | 1.3–1.5% in flow, 1.3–1.8% across flow on test plaques (about 0.95% on one nucleated grade) | ISO 294-4 |
Typical ranges from published ISO data sheets for Zytel 101L and 103HSL, Ultramid A3K and A3W, Vydyne 21SPC and 22HSP, and Akulon S223-D. Values are dry as molded unless marked conditioned. Your grade's own data sheet and the lot COA are what count.
What it’s used for
- Cable ties and wire harness clips
- Gears, bushings and bearings under light load
- Fasteners, clips, rivets and spacers
- Electrical connectors and terminal parts that need UL 94 V-2
- Automotive clips, fittings and fluid connectors (heat-stabilized grades near the engine)
- Appliance, furniture and sporting goods hardware
How to tell grades apart
- Dry as molded vs. conditioned. ISO sheets list both columns. Conditioned values are measured after the test bars take up moisture to equilibrium with 23°C / 50% RH air, which for PA66 means about 2.3–3.1% water. Celanese lists Zytel 101L at a tensile modulus of 3,100 MPa dry and 1,400 MPa conditioned. Compare dry with dry and conditioned with conditioned.
- Lubricated. A lubricant or release agent helps the pellets feed and the parts eject. Zytel 101L lists a release agent, and Ascend describes Vydyne 21SPC as internally and externally lubricated. An unlubricated grade can stick and eject differently in the same mold.
- Heat stabilized. For parts that live hot for years, such as under-hood fittings. Examples are Ultramid A3W, Vydyne 22HSP and Zytel 103HSL. Short-term heat deflection barely changes. What changes is long-term heat aging, so compare the producer's temperature index on the same basis (BASF lists 109°C for A3W against 101°C for A3K at 20,000 h).
- Nucleated. Nucleated grades set up faster for shorter cycles. Envalior's Akulon S223-D lists a higher tensile modulus (3,600 MPa dry) and lower plaque shrinkage (0.95%) than standard grades, so check part size if you switch to or from one.
- Viscosity. Nylon is sold by viscosity, not melt flow. The standard injection grades checked all list a viscosity number of about 150 cm³/g (ISO 307). Some U.S. sheets give relative viscosity instead. Match the number and method on your current sheet.
- Toughened is a separate family. Impact-modified PA66 such as Zytel ST801 lists about 80 kJ/m² notched Charpy dry, against 5–6.6 kJ/m² for unfilled grades, with lower stiffness and a lower density of 1.08 g/cm³. Do not swap one for the other without a part trial.
What to put on your RFQ or PO
- Resin and type. Unfilled PA66, injection molding, and which additives: lubricated, heat stabilized, nucleated or none.
- Viscosity. Viscosity number (ISO 307) or relative viscosity (ASTM D789), copied from your current data sheet with its method.
- Dry or conditioned values. Say which column your print or spec uses for tensile, modulus and impact.
- Flammability. UL 94 V-2 at your thinnest wall, if needed. UL listings are grade- and color-specific.
- Color. Natural, black or a match, and whether you add masterbatch at the press.
- Agency and specs. The producer's FDA letter (21 CFR 177.1500) for food-contact parts, and any ASTM D4066 callout or automotive spec on the drawing.
- Moisture as shipped. Ask what moisture the lot ships at and whether it is reported on the COA.
- COA values to check. Viscosity and moisture on every lot, plus color values for pre-colored resin.
- Packaging and quantity. Gaylords with moisture-barrier liners or sealed 25 kg (55 lb) bags, total quantity and release size.
A polymer chemist reviews every request and checks the grade against your process before we quote. Every prime lot from our suppliers ships with a COA, and orders start at one gaylord.
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- Same polymer, viscosity and additive package from another producer. The closest swap. Zytel 101L, Ultramid A3K and Vydyne 21SPC are reference points to check, not identical grades: BASF's A3K sheet does not state a lubricant, for example. See Zytel 101L equivalents and how to find an equivalent grade.
- Nylon 6. Melts about 40°C (72°F) lower, with lower heat deflection and an easier surface finish. See nylon 6 vs. nylon 66.
- PA66 with glass fiber. When the part needs stiffness and heat more than toughness. See PA66 30% glass.
- Acetal. Takes up far less water, so parts hold size in humid service. See acetal vs. nylon.
- PPA. Higher heat and lower moisture uptake at a higher price. See PPA vs. PA66 and PA66 alternatives.
Common processing problems
- Parts grow or change stiffness after molding: nylon swelling moisture
- Silver streaks from wet resin: splay silver streaks
- Flash on parting lines and vents: flash
- Brittle parts straight off the press: brittle cracking parts
- Size changes from shot to shot or lot to lot: dimensional variation
Common questions
Does nylon 66 need to be dried before molding?
Usually, once the bag or gaylord liner has been opened. Celanese gives about 80°C / 176°F for 2–4 hours in a dehumidifying dryer, to 0.2% moisture or less, for Zytel 101L. Ascend says Vydyne 21SPC can run without drying from an unopened bag. Follow the sheet for your exact grade, and do not over-dry, since long hot drying can discolor nylon.
What does conditioned mean on a nylon 66 data sheet?
The test bars have taken up moisture to equilibrium with air at 23°C and 50% relative humidity, about 2.3–3.1% water for PA66. Conditioned bars are less stiff and much tougher than dry ones. Parts in service end up somewhere between the two columns, depending on humidity and wall thickness.
What is the melt flow of nylon 66?
Most PA66 sheets do not give an MFR. They give a viscosity number (about 150 cm³/g by ISO 307 for standard injection grades) or a relative viscosity. BASF also lists MVR at 275°C / 5 kg: 120 cm³/10 min for Ultramid A3K and 100 for A3W. Compare viscosity to viscosity using the same method.
Are Zytel 101L, Ultramid A3K and Vydyne 21SPC interchangeable?
They are close in density, viscosity and dry properties, so they are common grades to compare, but they are not identical. Lubricant and stabilizer packages, color and agency listings differ. If your drawing names one grade, any change needs your approval and usually a part trial.
Tell us the grade you run now
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province