Linda Friesen uses polymorph plastic to create amazing prices for her couture fashion line. This shows what can be done with a polymer plastic with a hardener, freeform over a mannequin or person wrapped in plastic.
EVA Foam is a great material for constructing costumes and props of all different kinds, from period armor and swords to slick futuristic robots. It is especially beloved by cosplayers and prop makes (Diy Costume Ideas)
This woman's tutorial/walk-through on how she made her costume wings is *amazing*. Awesome creativity, and some pretty amazing engineering! Perfect for cosplay (I absolutely have to make a set of these wings)