The Material Question

Terry Pratchett's Discworld was full of objects that seemed to have minds of their own — swords with grudges, luggage with legs. Borrow that idea for a second and it feels true here too: every object carries a decision that was made before it existed. A designer decided it should bend instead of break, or break instead of bend. Decided it should survive a hot car, a dishwasher, a drop onto tile. You never see that decision — you only see the object, already committed to whatever it was built to survive.

Custom printing puts that decision back in your hands, which means it's worth understanding what you're actually choosing between.

PLA — the default, and a good one

PLA is where almost every 3D printed object starts, and for a lot of parts, it's also where they should stay. It's rigid, holds fine detail well, and represents 3D printing at its simplest — practically any printer built in the last few years handles it without complaint.

Think of PLA as the material for things that live in temperate, indoor, relatively controlled conditions — and for proof-of-concept prints, where the goal is testing a design cheaply before committing to a tougher, pricier material. As a rule of thumb: don't leave PLA anywhere hotter than a warm room for any length of time, and never in a closed car in the summer — that's well past the point where it starts to lose its shape.

Resin — beautiful and brittle

Resin is a different process entirely: liquid photopolymer cured layer by layer with light, rather than extruded from a spool. It buys extraordinary detail and glass-smooth surfaces that FDM plastics can't match. The trade-off is real, though — cured resin is typically stiff but brittle, closer to glass than plastic in the way it fails: it cracks or shatters under stress rather than flexing first.

PETG — the all-rounder

PETG gives up a small amount of PLA's rigidity in exchange for real toughness and much better heat resistance. It flexes slightly before it fails instead of snapping outright, resists moisture plus most household chemicals, and tolerates warm environments that would ruin a PLA masterpiece. It prints slightly less cleanly than PLA — it can string between features if the settings aren't dialed in — but nothing about it demands special equipment.

If you're not sure which material your part needs, PETG is usually the safer guess. It's the material that answers "what if it gets left in the car" before you have to ask.

ABS / ASA — built for the outside world

This is where a more specialist printer stops being a nice-to-have, and you're into enthusiast or semi-professional territory. Both materials shrink unevenly as they cool, and without steady, controlled temperature through the print, parts warp, crack, or simply move in ways that ruin the result. Handled properly, though, this is the toughest, most heat and UV resistant material family here — ASA in particular is built to sit outside for years without going brittle or chalky.

The tradeoff, at least, is honest: harder to work with, but it copes with the sun far better than most of us do.

TPU — the flexible outlier

TPU isn't rigid at all — it's rubber-like, shaped to bend, compress, and spring back rather than hold a fixed shape. Not all TPU behaves the same way: softer formulations feel closer to a stress ball, firmer ones closer to a phone case bumper, and the part's design — wall thickness, infill pattern — changes how it flexes and feels just as much as the material spec. It's genuinely resistant to light punctures too — press a pin into it and, within reason, it closes back up rather than staying visually damaged.

It does ask for a bit more patience than the materials above — a slower, more careful pass through the process rather than a quick one. It's more of a specialist tool than a general one: nobody's asking for a rigid bracket in TPU.

Specialty & composite filaments

Beyond the everyday materials, there's a growing family of composites — metal-fill, wood-fill, marble effect, carbon fibre and glass fibre reinforced — that blend a base plastic with particles that change how it looks, feels, or performs. Worth a specific mention for the RC and drone crowd: LW-PLA (light-weight, foamed PLA) is the go-to when a part needs to be strong but as light as possible — a world where every gram is weighed and argued over.

These materials open up genuinely different finishes and mechanical properties, but most are also abrasive to print with, which shapes some of the equipment decisions behind the scenes. They deserve their own proper treatment rather than a paragraph each — that's coming in later posts on The Craft.

The material question

The question isn't "what's the best material" — there isn't one. The question is what's the most appropriate material, or mix of materials, for the specific part being made. Every material on this list earns its place somewhere.

Choosing well just means asking the question honestly before you print.