Impact-modified nylon: toughened, super-tough and glass-filled impact-modified PA66 and PA6

Toughened, super-tough and glass-filled impact-modified: the generic tiers

Every impact-modified nylon works the same way. Fine rubber particles, bonded to the nylon, start many small yield zones ahead of a crack and soak up its energy. More rubber gives more toughness, and less stiffness, strength and heat deflection. Producers label the result in their own words: toughened, medium-toughened, high-impact or super-tough. ISO codes on data sheets add an I or HI for impact-modified; one super-tough PA66 sheet lists PA66-I in its ISO 16396 designation and PA66-HI as its resin code. The term super-tough is best known from DuPont’s Zytel ST grades, and DuPont patented rubber-toughened nylon compositions in the 1970s (U.S. Patent 4,174,358). Celanese has owned the Zytel brand since it completed its purchase of DuPont’s Mobility & Materials business on November 1, 2022. Other producers and compounders sell their own super-tough and toughened families, so treat the words as a family name and buy on the numbers.

Example values come from individual producer data sheets and are typical values, not specifications. ASTM D256 values (J/m or ft-lb/in) and ISO 180 or ISO 179 values (kJ/m²) do not convert into each other. Confirm on the data sheet for the grade you run.

Reading impact data: dry as molded vs. conditioned

Nylon takes up water from the air, and water makes it tougher and less stiff. So every impact number for nylon needs three things next to it: the test, the temperature and the moisture state. See Izod vs. Charpy impact for the tests themselves.

• ASTM D256 notched Izod. A 3.2 mm (1/8 in) bar, usually at 23°C / 73°F, reported in J/m or ft-lb/in (1 ft-lb/in = 53.38 J/m). U.S. data sheets mark the moisture state as DAM (dry as molded) or 50% RH.
• ISO 180/1A notched Izod and ISO 179/1eA notched Charpy. An 80 × 10 × 4 mm bar, reported in kJ/m². ISO sheets give a dry column and a conditioned column, conditioned to equilibrium at 23°C / 73°F and 50% relative humidity.
• Conditioning raises room-temperature impact. On one super-tough PA66, notched Izod (ISO 180/1A) rises from 80 kJ/m² dry to 90 conditioned, and notched Charpy (ISO 179/1eA) from 80 to 115. Flexural modulus falls by more than half on the same sheet (ISO 178: 1,800 to 700 MPa).
• Parts in service sit somewhere in between. A part molded in a dry plant in winter and shipped the same week behaves close to dry as molded. Write the moisture state you test in onto the print and the RFQ.
• Compare like with like. A conditioned value from one supplier against a dry value from another can make an ordinary grade look super-tough.

Cold impact at −40°C / −40°F

Rubber keeps nylon tough below freezing, but impact still falls as the part gets colder. ISO data sheets commonly add a value at −30°C / −22°F, and many sheets add −40°C / −40°F. Here is what single-producer examples show:

Typical values from individual data sheets and distributor listings of them, not minimums. The listings for the two heat-stabilized grades give one value per temperature without stating the moisture state.

• Super-tough grades lose most of their room-temperature value by −30°C / −22°F, but in these examples they still sit above the toughened grade at −30°C and −40°C (−22°F and −40°F).
• The moisture bonus mostly disappears in the cold. Conditioned values at −30°C / −22°F are equal to, or slightly below, the dry values on these sheets.
• Impact-modified glass-filled grades gain little in the cold on these sheets. The PA6 GF30 IM lists 11.4 kJ/m² dry at −30°C / −22°F, against 11 for the same producer’s standard PA6 GF30.
• Ask for data at your lowest service temperature. Outdoor parts in Canada and the northern U.S. can see −30 to −40°C (−22 to −40°F). Drop-test molded parts cold, since corners, ribs and weld lines matter more than the bar value. See the best plastic for cold temperatures.

Impact modifiers: EPDM-g-MA, POE-g-MA and ionomers

Plain rubber does not stick to nylon, so it pulls out of the matrix and does little. The modifier needs a reactive or polar group. Maleic anhydride grafted onto the rubber reacts with nylon’s amine end groups, which bonds the rubber in place and keeps the particles small. See maleic anhydride grafted polyolefins for graft levels and how they are measured.

• EPDM-g-MA and EPR-g-MA. Maleic anhydride grafted EPDM or ethylene-propylene rubber, the classic route to super-tough PA66 and PA6. One producer’s EPDM-based grades list about 0.4–0.6% and 0.8–1.2% maleic anhydride.
• POE-g-MA. A grafted ethylene-octene or ethylene-butene plastomer. It comes as free-flowing pellets, which makes it easy to feed, and is widely used by compounders for toughened nylon and impact-modified glass-filled grades.
• Ionomers. Ethylene acid copolymers partly neutralized with a metal such as zinc or sodium. They are polar and bond to nylon: DuPont’s original 1970s toughened-nylon patent used a zinc-neutralized ethylene terpolymer ionomer among its tougheners, and ionomers still show up in some toughened blends. See acid copolymers and ionomers.
• How much. High-impact and super-tough grades often carry about 10–25% grafted elastomer. Toughened grades carry less.
• Dispersion matters as much as the amount. The same loading gives very different impact if the particles are coarse or poorly bonded. A compounded grade with a data sheet is more consistent than a modifier tumble-blended at the press.

Swirl, flow lines and other surface issues

Toughened nylons show surface defects more often than unmodified grades. Common ones are matte or pearly swirls near the gate, flow lines and dull bands across the flow, haze on dark colors, and a skin that flakes or peels when the rubber is poorly dispersed or the melt runs too hot. The rubber particles stretch at the flow front and freeze into the skin, so anything that changes the flow front changes the look.

• Dry fully first. Splay from wet resin looks a lot like swirl. Rule it out before you change the process. See splay and silver streaks.
• Stay inside the producer’s melt range. Too hot a melt or too long a residence can degrade the rubber and the stabilizers.
• Work on fill speed and mold temperature. A slower start through the gate and a warmer mold within the producer’s range often calm swirl and flow lines. See flow lines and flow marks.
• Gate and vent. Generous gates and good venting cut shear and trapped gas.
• Peeling or flaking skin. Points to poor dispersion or contamination, not just settings. See delamination.
• Ask for a surface grade. Some toughened grades are made for appearance, and black hides more than natural. Compare the full data sheets before you switch.

Moisture, drying and conditioning

Impact-modified nylon dries like the base nylon. Use a dehumidifying dryer at about 80°C / 176°F, 2–4 hours for PA66 from a fresh bag and 2–6 hours for PA6. One super-tough PA66 data sheet gives 80°C / 176°F and 2–4 hours in a dehumidifying dryer, with moisture at 0.2% or less for molding and 0.06% or less for extrusion. Limits differ by producer and process, so use the one on your grade’s own sheet. Do not over-dry: it can yellow the resin and raise melt viscosity. See the resin drying chart.

Molding wet is worse for an impact grade than for most parts, because the damage is to toughness, the very thing you paid for. Water at melt temperature cuts nylon chains, and the parts can look perfect and still break. After molding, the reverse happens slowly: parts take up moisture, grow a little and get tougher. Some molders condition parts such as cable ties in humid air or water before packing for that reason. See nylon parts swelling from moisture.

Heat stabilization and service temperature

• Super-tough grades have low HDT under load. One super-tough PA66 lists 64°C / 147°F at 1.8 MPa (71°C / 160°F annealed) and 132°C / 270°F at 0.45 MPa (ISO 75). Its UL relative thermal index is 85°C / 185°F for strength and 75°C / 167°F for impact. None of these is a service rating on its own. See HDT vs. continuous use temperature.
• Pick the stabilizer type, not just the letters HS. Copper-halide packages are common in black under-hood grades. Organic (phenolic or amine) packages suit natural and light colors, and some electrical customers avoid halide stabilizers near metal contacts.
• Ask for heat-aging data on impact, not just tensile. The rubber phase can age in hot air, so retained impact after hours at your temperature tells you more than a tensile curve. Heat-stabilized toughened and super-tough grades exist for this.
• Outdoor parts. Ask for UV-stabilized black. See UV-resistant plastics.
• Flame rating. Most impact-modified grades are UL 94 HB; one super-tough PA66 lists HB at 0.81 mm. If the part needs V-0 or V-2, that is a different grade. See choosing an FR grade.

Cable-tie and fastener grades

Most cable ties are molded from unfilled PA66, often lubricated and nucleated for fast cycles, often heat-stabilized, and in UV-stabilized black for outdoor use. Thin straps fill long, narrow cavities, so tie resins are easy-flow injection grades. Ties are often UL 94 V-2 at the listed thickness. Impact-modified PA66 is common for cold-climate ties. Nylon 66 takes up water, and a dry tie is stiffer and more brittle, so tie makers manage moisture after molding and in packaging. UL’s application guide notes that ties are tested once the material reaches equilibrium moisture content.

• The tie is certified, not the resin. UL 62275 in the U.S. and CSA C22.2 No. 62275 in Canada are based on IEC 62275 and cover cable ties and fixing devices for electrical installations. The tie maker declares the ratings, such as loop tensile strength and minimum and maximum operating temperature, and a certifier tests the tie against them. UL 62275 took over the cable-tie requirements that used to sit in UL 1565 (positioning devices).
• Type 1 and Type 2. According to UL’s application guide, Type 1 ties are tested to retain 50% of the declared loop tensile strength after environmental exposures, and Type 2 ties to hold the full declared value. IEC 62275 has only these two types.
• Type 11 and Type 21 (U.S. and Canada only). The extra “1” means the polymer has also been evaluated for long-term thermal performance (RTI) under UL 746B or CSA C22.2 No. 0.17, and for flammability with at least a UL 94 HB rating. For these types, the tie’s maximum operating temperature is tied to the resin’s own long-term rating. Types 2S and 21S are investigated for primary support of cable and flexible conduit, with a declared strength of at least 222 N (50 lbf).
• Why a listing is tied to one resin. A certified tie is evaluated as made from specific materials, and Type 11 and 21 ties also rely on the resin’s own RTI and flame rating. So a tie maker generally cannot switch to another PA66, even a close equivalent, without the certifier’s review. If you mold certified ties, send us the resin and color named in your file. We quote that grade, or tell you plainly that an equivalent would need a file change.
• Temperature ratings. Tie makers’ catalogs commonly rate heat-stabilized PA66 ties at about 105–115°C / 221–239°F continuous, against about 85°C / 185°F for standard nylon ties. The rating on your tie comes from your listing and the tests, not from the resin data sheet.
• Clips and fasteners. Push-in rivets, fir-tree clips and harness clips are often heat-stabilized PA66, toughened where the clip flexes at assembly or in the cold. Under-hood OEM specs name the heat-aging test. See best plastic for snap fits and automotive.

Uses, supply and what to put on the RFQ

Impact-modified nylon goes where a part must take a hit and still resist oil, grease or heat: power-tool and appliance housings, clips and fasteners, sporting goods such as ski, skate and bike parts, snowmobile and lawn equipment parts, cable ties and wire-harness hardware. Toughened, heat-stabilized and custom-color grades are often made to order on a producer’s or compounder’s schedule, so allow lead time. Domestic compounders make these grades, and we quote through our supply partners case by case, from 22+ partner warehouse locations, from one gaylord to a bulk truckload of about 40,000–50,000 lb. Every prime lot from our suppliers ships with a COA.

Price follows the base PA66 or PA6, plus the modifier, stabilizers, glass and compounding, so these grades do not move one for one with base nylon. PA66 supply has tightened at times when its key intermediate ran short. See the nylon page for what drives nylon prices, and PA66 alternatives if you need a fallback.

• Base polymer and tier. PA66 or PA6, toughened or super-tough, and glass content by ash for filled grades.
• Impact values with conditions. The test (ASTM D256, ISO 180/1A or ISO 179/1eA), temperature, and dry as molded or conditioned. Add the cold value if the part sees winter.
• The stiffness floor. The lowest flexural or tensile modulus the part can live with, dry and conditioned.
• Additive package. Heat-stabilizer type, UV, lubricant, nucleation and color.
• Approvals. OEM material spec, UL file (for listed ties), PPAP or customer approval tied to the current grade.
• Quantity and ship-to. This order, yearly use, ship-to city, and whether a qualified equivalent or imported resin is acceptable.
• COA values to check on arrival. Moisture, viscosity or melt flow on the producer’s scale, glass by ash if filled, and the lot number on every box. See what a COA is.

Common questions

If your grade is not listed, tell us what you run. We source commodity, engineering and specialty resins.