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The same CAD model printed in PLA, PETG or nylon gives three very different parts. One might snap, one might sag in a hot car, and one might last for years. Choosing a 3D printing material follows the same logic as any material selection, with two extra questions: can the printer handle it, and how does printing change its properties?
Start with the part, not the filament
Answer the five usual questions first.
- Function: a visual model, a fit check, a working prototype, a jig, or an end-use part?
- Load: how big, steady or repeated, and in which direction relative to the layers?
- Environment: the highest temperature the part will see, sunlight, water, oils, fuel, contact with food or skin.
- Cost and quantity: one part or a hundred? Material cost is usually small; print time and failed prints cost more.
- Manufacturability: does your printer have an enclosure, a hardened nozzle, a heated chamber? Does the part need supports, inserts or post-processing?
Printing changes the properties
A printed part is not a solid block of plastic. It is a bundle of extruded lines fused together, with walls around an infill pattern. Two consequences matter for design.
- It is anisotropic. In FDM, strength between layers is often well below the strength along them. Orient the part so the main tensile and bending loads run along the layers, not across them.
- Datasheet values are best cases. Figures measured on moulded test bars are higher than what a printed part achieves. Infill percentage, wall count, layer height and print temperature all change the result. Test a printed sample when the load matters.
FDM materials compared
Values are typical and vary between brands; heat deflection temperature (HDT) shows roughly when a loaded part starts to soften.
| Material | Strength and stiffness | Toughness | Heat (HDT, approx.) | Environment | Printing | Good for |
|---|---|---|---|---|---|---|
| PLA | Stiff, good strength | Low, brittle | about 55 °C | Indoor only; softens in sun and in cars | Easiest, no enclosure | Visual models, fit checks, low-load prototypes |
| PETG | Good | Good | about 70 °C | Water and many chemicals; fair UV | Easy; can string | Functional parts, brackets, covers, light outdoor use |
| ABS | Good | Good | about 95–100 °C | Indoor; yellows in sun | Needs enclosure; warps | Housings, heat-exposed parts, parts to smooth with acetone |
| ASA | Similar to ABS | Good | about 95–100 °C | Excellent UV and weather resistance | Needs enclosure | Outdoor parts, car exteriors, enclosures |
| Nylon (PA) | High strength, flexible | Very high | about 70–180 °C depending on grade and fill | Oils and fuels; absorbs moisture | Must be dried; enclosure helps | Gears, hinges, snap fits, wear parts |
| Carbon-fibre-filled nylon or PETG | Very stiff | Medium | Higher than unfilled | As base polymer | Hardened nozzle needed (abrasive) | Jigs, fixtures, stiff brackets |
| Polycarbonate (PC) | Very strong | High | about 120–140 °C | Good | Hot nozzle and chamber; warps | Strong, heat-resistant functional parts |
| TPU (flexible) | Rubber-like (Shore 85A–95A) | Excellent | Moderate | Oils, abrasion | Slow printing | Seals, grips, bumpers, flexible couplings |
Resin, powder and metal printing
- SLA and DLP resins give the finest detail and smoothest surfaces. Standard resins are brittle; tough, high-temperature, flexible and castable resins exist for specific jobs. Most degrade slowly in sunlight.
- SLS nylon (PA12, PA11) gives strong, nearly isotropic parts without supports, ideal for small production runs of functional parts.
- Metal powder bed printing (316L stainless, AlSi10Mg aluminium, Ti-6Al-4V titanium, 17-4PH stainless) makes dense metal parts close to wrought strength after heat treatment, at a much higher cost.
Worked example: a phone holder for a car dashboard
Function: holds a phone; light load, but it must not creep or droop. Environment: a parked car’s dashboard in summer can reach 70–80 °C or more, in direct sunlight. Quantity: a handful of parts.
Screen: PLA (HDT about 55 °C) would sag on the first hot day. PETG (about 70 °C) is borderline. ABS and ASA (about 95–100 °C) have margin, and ASA also resists UV.
Check manufacturing: ASA needs an enclosed printer to avoid warping, which is available.
Designing for the material you print
- Walls: at least 3 perimeters (about 1.2 mm with a 0.4 mm nozzle) for strength; walls carry more load than infill.
- Holes and fits: printed holes come out slightly small; leave 0.2–0.3 mm clearance for sliding fits, or print undersize and drill or ream.
- Threads: use heat-set brass inserts or captive nuts rather than printed threads for parts that are assembled more than a few times.
- Overhangs: faces up to about 45° from vertical print without supports; design chamfers instead of flat overhangs where possible.
- Orientation: decide it in CAD, with the load direction, so the drawing or print note can state it.
Specifying it on the drawing
A printed part’s drawing or print note should state more than “PLA”: the material and brand or grade, colour, process (FDM, SLA, SLS), layer height, wall count, infill, orientation, and any post-processing such as inserts, annealing or painting. That way the part can be printed again with the same properties.
Key points
- Choose from function, load, temperature, environment and printer capability.
- PLA for models, PETG for general functional parts, ASA outdoors, nylon for tough and wear parts, PC for strength and heat.
- FDM parts are weakest between layers; orient them for the load.
- Specify process settings along with the material so the part can be reproduced.