10.9  Filament materials

The common filaments compared as a designer chooses between them: PLA, stiff, easy to print and soft at about 60 °C; PETG, tougher and better near warmth; ASA and ABS for heat and sunlight, at the price of warping; TPU for parts that must stretch; PC and the nylons for strength and temperature, which need a dry filament and an enclosed printer; and the fibre-filled grades, stiffer and more brittle, which wear a brass nozzle. For each we give the modulus, the strength along and across the layers, the strain at the peak, the glass transition temperature, and what the material asks of the printer. Datasheet values come from moulded or specially printed specimens and are reported as such; our own come from the cohort tensile lab, where groups print PETG, X-PLA and fibre-filled grades against the same PLA reference. Two material effects on the process close the chapter: moisture, which ruins a print before it ruins a part (the cage of the printed bearing printed wet), and shrinkage, which warps large flat parts and is designed against with volume and rounded edges. Sliding and friction are treated briefly: a printed plastic makes a poor brake lining and a fair slow pivot.