by daremo
I echo what pluv said, smooth-on is highly recommended for anything resin casting related. My goto resin for flexible helmets and webgear would be task 14. You need a gram scale for mixing and it starts curing pretty quick. It only comes in black unfortunately, although I’ve had success adding white tint to make it gray.
Task 14 could work for hair too, but you would have to paint it if you wanted to do other colors. There’s also Specialty Resin that have a similar resin (Flex-it 90) to Task 14 that’s semi clear and works with tints. It cures much quicker than Task 14 but if you want a flexible part in a specific color, it’ll do. They have other slower curing semi clear flexible resins but I’ve only used the 90.