“Sometimes one may require a non-planar mirror. Usually you can do that by turning and polishing a chunk of metal on a lathe until it is so smooth that the metal works like a mirror. Or you can achieve a mirror surface by grinding a piece of glass or coating plastic in a vacuum chamber. All of that is pretty slow and expensive.
But is there maybe an easier or faster way at the cost of a bit of precision? (yes)
The material I use is laminated and metalized polystyrene. Since there is already a mirror surface on the material we don’t need to coat it as a second step. And as a thermoplastic is easily deformable and at room temperature pretty stiff so it keeps its shape.
Before I settled on Polystyrene I did a quick test of different mirror-like materials:
Coated acrylic glass
PVC foil with an aluminium layer
and Rustoleum Mirror Spray on a PETG sheet
Comparing this works pretty easy by bouncing light against different mirror materials onto a sheet of paper. My reference material is a silver-coated glass mirror, which is pretty standard stuff and the highest quality mirror you’ll find in your household.”