Most armor costumes you see (ex: Iron Man, Mass Effect, etc) are made of EVA Foam, cut and glued together, dremmeled for weathering, and painted. It's flexible, strong, formable, and cheap. EVA is commonly used in interlocking foam floor tiles from hardware stores, automotive centers, and even discount stores like Big Lots or used in yoga mats. It doesn't matter what color, you're going to paint it anyway! Mad props to BioWeapons for creating the happiest set of armored boobs I've ever seen!
Cheap silicone mold making instructions. You will need: water blue dish-soap(about 1 oz per pint water clear 100% silicone caulk (do not buy quick set silicone, you need 100% silicone) bowl caulk gun scissors/knife