Why material choice drives the whole project
Choosing the right engineering plastic is the single decision that most shapes a prototype's cost, lead time, and how closely it predicts the final product. A part that is strong enough on the bench can still fail in the field if the material softens under heat, creeps under load, or cracks on contact with a cleaning agent. Material is function, not just appearance.
The five workhorses—ABS, PC, POM, PA, and PEEK—cover the overwhelming majority of prototype needs. Each sits at a different point on the triangle of cost, temperature resistance, and mechanical strength. Learn where each one lives and you can spec a part in minutes instead of guessing and re-printing.
ABS: the cheap all-rounder
ABS (acrylonitrile butadiene styrene) is the default cheap all-rounder. It machines and bonds easily, paints and plates well, and stays dimensionally stable up to about 80 °C. For most enclosures, jigs, and non-critical brackets, ABS is the fastest path to a usable prototype at the lowest cost.
ABS is also the friendliest plastic to post-process: it can be vapor-smoothed for a glossy surface, solvent-welded, and glued with common adhesives. Its weaknesses are low continuous-service temperature and poor resistance to many solvents and UV unless graded for outdoor use. Pick ABS when budget and speed matter more than heat or chemical exposure.
PC: clarity and impact strength
Polycarbonate (PC) brings two things ABS cannot: high optical clarity and excellent impact strength. A PC window or lens stays transparent while shrugging off drops that would shatter acrylic. It holds shape to about 120 °C and is a common choice for transparent housings, safety covers, and snap-fit enclosures.
PC is tougher to machine than ABS because it can gum up tooling and crack under internal stress if cooled wrong. It also scratches more easily and yellows under long UV exposure unless UV-stabilized. Use PC when you need see-through parts, high impact resistance, or both—and budget a bit more for finishing.
PA (nylon): tough and slippery
PA, or nylon, is the tough, slightly flexible family that absorbs impact and resists a wide range of chemicals. Its self-lubricating, low-friction surface makes it ideal for gears, rollers, and wear pads that move against metal or plastic. Filled grades (glass, carbon) push its stiffness and temperature ceiling higher.
The catch is moisture: nylon absorbs water from the air, which swells the part and shifts its dimensions over days or weeks. For functional fits you must either design around the swell or condition the part before measuring. Choose PA when you need toughness, sliding wear, or chemical resistance more than tight, stable dimensions.
POM (acetal): precision and low friction
POM (acetal, also called Delrin) is the precision plastic. It is dimensionally stable, has very low friction and high fatigue resistance, and machines to a beautiful finish. Bushings, cams, gears, and snap components made from POM run quietly and last long because the material does not creep or cold-flow easily.
Unlike nylon, POM barely absorbs moisture, so its size stays put—a big advantage for tight-tolerance moving parts. It is stiff rather than tough, so it can crack under sharp impact rather than bend. Reach for POM when you need accurate, low-friction, repeatable motion in a part that must hold its shape.
PEEK: the heat champion
PEEK (polyether ether ketone) is the heat champion of the group. It retains strength and shape above 250 °C, resists most chemicals including steam and automotive fluids, and is approved for repeated medical sterilization. Where other plastics melt or creep, PEEK keeps working—under the hood, in sterilizers, in downhole tools.
PEEK is expensive and demanding: it needs high-temperature 3D printing or CNC with sharp, well-cooled tools, and it machines with care to avoid heat damage. Reserve it for parts that genuinely face extreme heat, aggressive chemicals, or regulatory sterilization. For everything else, a cheaper plastic will do the job.
Match the material to the requirement
Start the selection by listing the real demands: continuous temperature, peak load, chemical contact, sliding wear, and whether the part must be transparent. Then walk the ladder—ABS for benign conditions, PC for clarity and impact, PA or POM for wear, PEEK only when heat or chemistry rules out the rest.
Do not over-specify. A bracket that never sees heat does not need PEEK, and a gear that must hold a tight bore should not be nylon unless you plan for moisture swell. Matching the material to the actual duty, not the worst imaginable case, keeps cost and lead time where they belong.
Process compatibility: CNC vs 3D printing
All five machine cleanly on CNC, which is the surest way to get accurate, isotropic parts in the real material. For 3D printing, ABS and PA suit FDM; PC and PEEK need enclosed, high-temperature printers with dry filament and a heated chamber to avoid warping and delamination.
SLA and other resin processes can mimic the look of several of these plastics for visual prototypes, but they do not carry the real mechanical or thermal properties. If the prototype must function under load or heat, print or machine in the actual engineering plastic rather than substitute a look-alike resin.
Moisture, finishing, and validation
Plan for the material's quirks before you measure or assemble. Nylon parts should be conditioned and re-measured after they stabilize; PC and ABS benefit from stress relief; PEEK demands tight thermal control during both making and any post-machining. Ignoring these steps is the usual cause of 'it fit yesterday, not today'.
Finishing also differs by material. ABS vapor-smooths, PC polishes to clarity, POM takes a clean machined gloss, while PEEK usually ships as-machined. Tell your shop the end use so they pick the right stock, drying, and surface treatment—and always validate a critical fit with the production-intent material, not a stand-in.
Typical applications by industry
Consumer and robotics teams lean on ABS and PC for enclosures, jigs, and transparent windows during development. Automotive and industrial use PA and POM for gears, guides, and bushings that must survive motion and light chemical exposure.
Medical and aerospace reach for PEEK where sterilization or heat rules, and for lightweight brackets that still need real strength. Semiconductor and food equipment value POM and PEEK for their low outgassing and chemical resistance. Match the industry pattern, then adjust for your specific duty cycle.
Decision checklist and FabProto support
A material selection checklist: what is the continuous temperature? What load and impact must it survive? Any chemicals or cleaners? Does it slide or stay still? Must it be clear? Start at ABS and climb only as duty demands—PEEK last, and only when nothing cheaper qualifies.
FabProto stocks and machines all five plastics and prints the print-capable ones in-house. Send your CAD and duty requirements and we will recommend the right material, warn you about moisture or heat limits, and deliver a part in the actual plastic your production will use. That way your prototype proves the real design, not just a shape.