A keycap is injection-moulded to tolerances of a few hundredths of a millimetre, and you slowly destroy one every few million keystrokes without noticing. It starts with polymer choice, and the two candidates behave nothing alike in the mould. - ABS is amorphous. It flows beautifully, captures fine mould detail, and shrinks only 0.4 to 0.7 per cent on cooling. Its weakness is the surface: polymer chains abrade under a fingertip until the texture polishes into that greasy shine. - PBT is semi-crystalline. Higher melting point, better solvent resistance, a drier and grainier feel. But crystallisation means it shrinks 1.5 to 2 per cent, so the steel cavity is cut deliberately oversize: the mould-maker must predict the final part before it exists. Molten polymer enters the tool near 250 degrees, is packed under holding pressure to fight shrinkage as it solidifies, then ejected in seconds. Then the harder problem: putting a legend on it that survives. - Pad printing: a silicone pad lif...