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Engineering Thermoplastics

Engineering thermoplastics — nylon (PA6, PA66, PA12), acetal (POM), polycarbonate (PC), PBT, PET and acrylic (PMMA) — are the tier where plastic parts start carrying load: tensile strengths of 60–90 MPa unfilled, up to about 150 MPa glass-filled, and continuous service from about 80 to 150 °C. They mold, machine and print well, and they are what most functional gears, bushings, housings, lenses and snap-fits are made of.

Popular engineering thermoplastic grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityBest for
POM-C63651.41ExcellentPrecision gears, bushings, machined fits
PA675801.14GoodTough machined and molded parts; rollers, pads
PA6680821.14GoodStiffer, hotter nylon for gears and sprockets
PC63681.2GoodImpact-resistant guards, covers, clear parts
PMMA68701.19Very goodScratch-resistant optical windows and displays
PA1240481.01GoodSLS and MJF printed functional parts
UHMW-PE21400.94Very goodSliding wear strips, liners, impact pads

All 82 engineering thermoplastic grades

Choose engineering thermoplastics for

Gears, bushings, cams and precision wear parts (POM-C, POM-H, PET); tough rollers, sprockets and pads (PA6, PA66, PA6G, UHMW-PE); impact-resistant housings, guards and lenses (PC, PC-ABS, PMMA, PETG); electrical connectors and bobbins (PBT, PBT-GF30); functional SLS and MJF parts (PA12, PA12-GF, PA12-CF); and any load-bearing plastic part that runs below about 120 °C.

Look elsewhere when

The part runs hot, wet and loaded above 150 °C or in hot solvents (PEEK, PPS, PEI in the high-performance tier), it must sit in fuel or hydraulic fluid (PVDF, PTFE), it is a commodity enclosure where ABS or PP is good enough, it needs the lowest friction against steel (PTFE or the PTFE-filled POM-C LF), or stiffness above about 10 GPa is essential — no unfilled plastic here exceeds 3–4 GPa; a carbon-filled grade or aluminum is the answer.

Tensile strength against max service temp, Engineering thermoplastics among every polymer grade

No materials in view have both of these properties.

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Engineering thermoplastic by application

Gears, bushings and precision fits
POM-C by default, POM-H when a little more stiffness and hardness helps; PET where the part must stay flat in humid service; PA66 for gears that must survive shock loads and can tolerate a little growth.
Tough rollers, pads and sprockets
PA6 and PA66 for abrasion and impact; PA6G cast nylon for large blocks, sheaves and bushings over about 100 mm; UHMW-PE for chute liners, wear strips and anything that sees sliding abuse.
Clear guards, lenses and covers
PMMA for optical clarity and scratch resistance (about 92 % transmission), PC where the guard may be struck (roughly 250 times the impact resistance of glass), PETG for thermoformed guards and printed clear prototypes.
Printed functional parts
PA12 on SLS and MJF for near-isotropic, near-molded strength; PA12-GF for stiffness, PA12-CF for the highest stiffness-to-weight; Alumide for a metallic look; ASA or PC-ABS on FDM for large outdoor or housing prototypes.

Working with engineering thermoplastic

Machining
POM-C, PET, PC and PMMA machine to ±0.05 mm with a clean finish; nylon is tougher and moves with moisture, so rough, let it rest, then finish. Avoid sharp internal corners in PC and PMMA (they craze under stress) and anneal machined POM, PC and PMMA before final measurement on tight-tolerance parts.
Molding and printing
POM and PA shrink about 2 % in the mold and need generous draft and uniform walls; PC and PBT shrink 0.5–0.7 %. Nylon must be dried below 0.2 % moisture before molding or printing. PA12 is the standard SLS and MJF powder; PC, ASA, PETG and PC-ABS print on FDM in a heated chamber; PMMA and POM do not print well.
Bonding and welding
PC, PMMA, PETG and ASA solvent-bond (methylene chloride, MEK) and take cyanoacrylate, acrylic and epoxy adhesives; PC and PA ultrasonic-weld well. POM and UHMW-PE bond to almost nothing — design mechanical fasteners, snap-fits or press fits, or use plasma treatment plus a primer.
Moisture and dimensional stability
PA6 absorbs up to about 3 % water at saturation (PA66 about 2.5 %, PA12 about 1.5 %) and grows roughly 0.5 % in size while gaining toughness; POM, PET and PC absorb under 0.5 % and hold dimensions. State dry-as-molded or conditioned properties on the drawing when nylon carries load.

Other polymer series

Engineering Thermoplastics — frequently asked

What is engineering thermoplastic?

Engineering thermoplastics — nylon (PA6, PA66, PA12), acetal (POM), polycarbonate (PC), PBT, PET and acrylic (PMMA) — are the tier where plastic parts start carrying load: tensile strengths of 60–90 MPa unfilled, up to about 150 MPa glass-filled, and continuous service from about 80 to 150 °C. They mold, machine and print well, and they are what most functional gears, bushings, housings, lenses and snap-fits are made of.

Which grade of engineering thermoplastic should I use?

POM-C for anything that must hold size and slide — gears, bushings, valve bodies, precision housings; POM-H (Delrin) is a little stiffer and harder. PA6 and PA66 when toughness and abrasion matter more than dimensional stability (rollers, wear pads, sprockets); PA6G cast nylon for large blocks and bushings; PA12 for printed SLS and MJF parts and for low moisture uptake. PC for impact and clarity (safety guards, light covers), PC-ABS as the molded housing compromise, PC-FR where UL 94 V-0 is needed. PMMA for optical windows that must resist scratching; PETG for formed and printed clear guards; PET for machined parts that must stay flat in humid environments; UHMW-PE for sliding wear and impact; ASA for outdoor housings.

Which grade of engineering thermoplastic is the strongest?

MXD6 has the highest yield strength in the series at 145 MPa; PA6T follows at 95 MPa. Values are for each grade's default condition.

Which grade of engineering thermoplastic is easiest to machine?

POM-H (machinability excellent, 90/100), then POM (88/100).

POM-C or POM-H (Delrin)?

POM-H homopolymer is about 10 % stiffer and harder (yield about 70 MPa versus 65 MPa) and slightly better in fatigue; POM-C copolymer has better hot-water and alkali resistance, less centreline porosity in thick sections and a wider molding window. For machined parts POM-C is the safer stock; specify POM-H when the drawing calls out Delrin or needs the extra stiffness.

PA6 or PA66?

PA66 melts at about 260 °C against 220 °C for PA6, is stiffer and holds strength about 20 °C higher, and absorbs a little less water. PA6 is tougher, easier to mold and cast (PA6G blocks), and cheaper. Use PA66 for gears, under-hood and electrical parts that run warm; PA6 for rollers, pads, sheaves and general machined nylon.