Choosing a prototype material: stiffness, heat, moving parts

Most material arguments with clients start from a question asked too late: where will this part actually live? A bracket that sits on a meeting room table can be printed in almost anything on the shelf. The same bracket left on a dashboard through July comes back to us as a sad curve with the screw holes pulled oval.

So before filament names come up, we ask how hard the part gets pushed, how hot it gets, and whether any surface on it slides against another. Those answers cut the list down faster than any comparison chart, because nearly every material that is good at one of them gives something up on another.

This page is about the material, not the route from file to part. If you are still getting geometry ready, how a design becomes a printed prototype covers that ground. Here we stay on the plastic.

What we ask before picking a prototype material

Load first. A part that only proves shape and fit needs nothing from the material except dimensional honesty. A part that holds a motor, carries a hinge, gets clamped in a fixture or gets handed around a trade show for four days is a different brief.

Temperature next, and in this city it is rarely the number people expect. Nobody is printing parts for ovens. The killer here is a car park.

Then friction. A surface that touches another moving surface wears, squeaks or binds, and plastics behave very differently once motion is involved. A material can be stiff and heat resistant and still make a terrible gear.

We also ask, more quietly, whether the part has to look finished or only to work. A test part can keep its layer lines and support scars. A part that goes in front of a client or a camera needs sanding, filler and primer, and some materials take that work much better than others.

Stiffness and load: what modulus means on the bench

Stiffness is how much a part deflects under a given push, and it comes from the material and from the shape. Shape usually wins. A 2 mm flat plate in the stiffest filament we stock will still flex in your hands; the same plate with a 4 mm rib across it stops flexing in anything.

That is why we push back when a client wants to fix a floppy part by changing material. Material swaps buy you a factor, geometry buys you a multiple. Adding a rib, thickening a wall from 2 mm to 3 mm, or turning a flat panel into a shallow dish moves deflection far more than going from PETG to polycarbonate.

Where material does decide the outcome is creep, the slow surrender of a loaded plastic over weeks. A clip that holds perfectly when you snap it on can be loose a month later with nothing visibly wrong. PLA is the worst offender in warm conditions; nylon and polycarbonate hold load over time much better. If your prototype sits preloaded or snapped shut for weeks, say so before we quote.

FDM parts are also weakest between layers rather than across them. A printed hook loaded in the direction that peels layers apart fails at a fraction of the force it survives when the layers run along the pull, so we orient functional parts for the load direction. When load arrives from two directions at once, that is usually where SLA or a redesign enters the conversation.

Heat: from an air-conditioned office to a parked car

A car interior parked in the sun reaches roughly 70 to 75 degrees on surfaces and trapped air, and summer street temperature alone gets to about 50. Those conditions decide more Dubai prototypes than any line on a datasheet. An office sits at 22, so a part that travels between the two takes the full swing, plus direct UV, plus humidity.

Glass transition temperature (Tg) is where a plastic starts softening. Heat deflection temperature (HDT) is where a loaded test bar bends by a set amount. Published figures from filament makers disagree with each other more than you would like, so treat them as bands rather than constants: PLA gives up somewhere around 50 to 60 degrees, ABS typically holds to around 90, PETG lands in a wide 80 to 95 range depending on grade and print settings, and polycarbonate sits far above all of them at roughly 140.

Put the car number next to the PLA number and the problem is obvious. We have had PLA parts come back from a month of commuting in a client's boot with every unsupported span drooping and every boss around a screw slumped. Those parts came off the printer clean; the plastic simply spent its afternoons above its softening point.

ASA deserves more attention than it gets, and almost nobody writing about prototype materials mentions it. Mechanically and thermally it sits close to ABS, but the formulation is built to survive UV and weather instead of yellowing and going chalky. For a part on a balcony, in a vehicle, in a sunlit window display or outdoors at an event, ASA is usually our answer. It pays for that with warping: it wants an enclosed printer, a hot chamber and a slow first layer, and large flat ASA panels still argue with the bed.

Friction and wear in moving parts

Gears, hinges, cams, sliding rails and anything with a bearing seat are a separate category. Hardness does not predict wear here, and the pair of surfaces in contact matters as much as either one alone.

Nylon is our default for printed moving parts. Low friction against itself and against metal, repeated impact without cracking, and wear that arrives slowly rather than suddenly. A nylon gear running on a metal shaft is the one combination we rarely worry about.

PETG is stiffer and easier to print, and it handles low speed, occasional motion. It also squeaks and polishes itself into a slightly loose fit after a few hundred cycles. PLA is hard and dimensionally precise, fine for a gear you need to demonstrate twice, but under continuous motion it heats at the contact point and then behaves exactly like a plastic above its Tg.

Worth knowing before you pay for a material change: on FDM gears, layer height often matters more than the plastic. A PETG gear that chews itself up at a 0.28 mm layer height frequently behaves at 0.12 mm with the hub axis vertical, because at the finer step the tooth flank sits much closer to the curve the CAD actually drew. The coarse version was failing on stair-stepped teeth, not on material.

Clearance is the other half of the job. For FDM pivots and sliders we typically leave in the region of 0.3 to 0.4 mm between moving faces; SLA parts hold much tighter gaps, often 0.1 to 0.2 mm, because the process puts less material where you did not ask for it. Those are starting points we adjust after the first fit, not rules.

FDM filaments compared

Our shelf for functional work is short on purpose: materials we understand well and can reprint identically next month beat variety. The processes we run across jobs are on our materials and technologies page.

• PETG. Default for a part that has to do something but lives indoors. Stiff enough, tough enough, prints reliably at large sizes, bonds well between layers, sands to a decent surface. It scratches, feels slightly rubbery under a file, and loses to ABS and ASA on heat under load.
• ABS. Better heat resistance than PETG, lighter, machines and sands beautifully, and it can be solvent bonded, which matters when a part arrives in sections. It warps while printing, needs an enclosure, and yellows and goes brittle in sunlight over months.
• ASA. What we use when the part faces sun and weather. ABS-level strength and heat behaviour with far better UV stability. Prints harder than ABS and needs more care on large flat geometry.
• Nylon (PA12). The choice for moving parts, living hinges, impact and anything that must not crack. High heat tolerance, low friction, absorbs punishment. Also the most demanding material here and more expensive, both in the spool and in the scrap rate while we dial a new geometry in.
• Polycarbonate. Serious heat resistance and serious toughness in the right geometry. It demands high temperatures and a hot enclosed chamber, and it punishes thin tall parts with warping. We reach for it when the heat requirement genuinely sits above ABS and ASA.

Nylon needs one warning, because it is the most common reason a part comes out the wrong size. It is far more hygroscopic than PETG, ABS or polycarbonate: it pulls moisture out of the air continuously, and Dubai air supplies plenty. Wet nylon flashes that water to steam in the nozzle, which gives a hissing print, rough surfaces, poor layer bonding and parts that measure differently from the file. We dry nylon spools in a filament dryer before every job, typically overnight, and keep them in a dry box while printing. Finished nylon parts keep absorbing moisture and can swell slightly over weeks, so critical nylon fits get checked at assembly, not just off the printer.

Carbon-filled filaments: when the stiffness is worth it

Carbon fibre filled PETG, nylon and ABS are stiffer than the base plastic, hold shape better under sustained load, warp less, and come out with a flat grey finish that looks expensive without paint.

You pay for that in brittleness and abrasion. A carbon filled part has less give before it cracks, so it is the wrong answer for a snap fit or a living hinge. The powder also eats brass nozzles, so these jobs run on hardened hot ends.

Carbon filled material earns its place on long flat fixtures that must stay flat, jigs that get clamped, structural inserts inside a larger printed shell, and parts photographed unpainted. It does not belong anywhere that flexes by design, anywhere with fine threads cut into the plastic, or anywhere a crack is worse than a bend.

SLA resins for compact functional parts

Most writing about resin treats it as decorative, which stops being true once parts get small and precise. Resin parts are effectively one solid piece rather than a stack of layers, so strength does not depend on orientation the same way. Fine detail survives: a 0.5 mm wall, a thread form, a small clip, a thin lever. Surfaces come off the printer closer to a moulded part, which matters when a prototype has to be seen as well as tested.

Tough and durable resin families are the ones we use for working parts, and they behave roughly like a tough engineering plastic: they bend before they break instead of shattering like standard resin. High temperature resins go much further. Formlabs publishes a heat deflection temperature of 238 degrees at 0.45 MPa for its High Temp Resin, though that top figure needs post curing plus a thermal treatment cycle; post curing alone gives 120 degrees on the same test. Read any resin heat claim with the processing step attached. High temp resin is brittle, so it suits hot and static work rather than hot and knocked about.

Resin has limits worth stating plainly. An under cured part is weaker and softer than the datasheet suggests, so post curing is not optional. And resin keeps reacting to UV after it leaves us, so a resin part living in sunlight gets more brittle and shifts colour over months. For small functional parts indoors, resin is often the best option available. For a part going on a dashboard, it is the wrong one.

How we choose on a real job

A fit check for an enclosure, used for a week in an office: PETG, or PLA if the deadline is tomorrow and the part never leaves air conditioning.

A hinged demonstration unit a sales team carries into meetings for three months: PETG body, nylon hinge pin and bushings, brass heat set inserts at every screw point. What fails in these is never the plastic, it is the screw holes after the twentieth open and close.

A sensor housing mounted on a vehicle: ASA, no discussion. UV plus the 70 to 75 degree cabin swing rules out PLA and PETG, and ABS will chalk and crack in that sun within months.

A gearbox mock-up with a working train: nylon gears printed fine, metal shaft, pressed bearings. If the module is too small for FDM to hold the tooth form, the gears move to tough resin and we accept a shorter service life on the prototype.

A part larger than the build volume: material gets decided together with the sectioning plan, because joint faces, dowels and adhesive depend on the plastic. ABS can be solvent bonded, PETG and nylon cannot in the same way, and nylon is the hardest of all to glue reliably.

What hand finishing fixes that material cannot

A fair amount of what clients want from a different material is actually a finishing job.

Threads are the clearest case, because printed threads in any plastic strip under repeat use. We drill and tap, or install brass heat set inserts with a soldering iron, and the screw joint is then as strong as the metal in PETG and nylon alike.

Bearing seats work the same way. We print the seat undersized, open it with a reamer to the measured bore, and press or bond the bearing in, which gives a running fit no printed hole achieves straight off the bed.

Mating faces that must sit flat get sanded on a flat plate rather than reprinted. A warped ABS panel edge usually becomes acceptable in ten minutes with 180 grit and a reference surface.

Surface finish is its own cycle: sand, fill the layer lines, prime, check the surface under a light at a low angle, then go round again. On exhibition and presentation pieces that loop runs several times before any colour goes on, which is why a well finished PETG part can look better than a premium material straight off the printer.

If your part has a load, a temperature and a moving surface in it, send the file or a sketch and tell us where it will live. We come back with a material, a print orientation and whatever hand work it needs, priced for that job. The contact form and WhatsApp number are on the site.

FAQ

What is the best 3D printing material for Dubai's hot climate?

For parts that see sun and vehicle temperatures, ASA is our usual answer: ABS-level heat resistance with UV stability built into the formulation. For heat without sun, ABS and nylon both work, and polycarbonate when you genuinely need to go above them. Treat PLA as an indoor, air conditioned material here. PETG sits in between: fine indoors and in shade, unreliable inside a parked car.

Why does nylon become brittle, and how does humidity affect it?

Nylon pulls moisture from the air faster than PETG, ABS or polycarbonate. Wet filament prints badly: the water turns to steam in the nozzle, leaving rough surfaces, weak bonding between layers and parts that measure differently from the file. Those defects are what make the part fragile, not the nylon itself. Dried and printed properly, nylon is one of the toughest materials we run. Finished nylon parts also take up moisture over time and can swell slightly, which matters on tight fits.

PETG or ABS for functional parts?

PETG is easier to print reliably, bonds better between layers and is tougher in thin sections, so it is our default for indoor functional parts. ABS wins on heat resistance under load, on weight, and on finishing, since it sands and solvent bonds better when a part arrives in sections. If sunlight is involved, ASA replaces both.

Which material should I use for printed gears and moving parts?

Nylon first, for low friction and slow wear. PETG is acceptable for low speed and occasional motion. Before changing material, check layer height and print orientation, because coarse layers on a tooth flank cause more trouble than the plastic does. For small gears with fine teeth, tough resin holds the tooth form better than FDM can.

Can an SLA resin part work as a functional prototype?

Yes, within limits. Tough and durable resins behave like a tough engineering plastic and hold detail FDM cannot reach, and they do not have the weak layer direction FDM parts have. The limits are UV exposure, which makes resin parts more brittle over months outdoors, and the need for proper post curing. For compact functional parts that live indoors, resin is often the best choice.

What is the difference between HDT and Tg?

Glass transition temperature is where a plastic starts to soften and lose stiffness. Heat deflection temperature is a test result: the temperature at which a loaded bar bends by a specified amount at a stated load such as 0.45 MPa. HDT is closer to service behaviour because it includes load, but both figures vary between manufacturers and print settings, so use them to compare materials rather than as hard limits.

What should I ask a print shop before ordering a functional prototype?

Tell them the operating temperature, the load and whether anything moves. Then ask what material they propose and why, which direction the part will be printed relative to the load, what hand finishing is included, and whether threads will be printed, tapped or fitted with inserts. Ask whether the part comes in one piece or in sections, and how the joints are made. The answers tell you more about a shop than any material list.