Ah, foam shaping. I did this tactic when I was making my Iron Man costume. Plan on making a new one in the future. I can also confirm that there was in fact, glue, time, and tears.
Actually depends on the thing you are trying to make. I used, I believe 3mm thick or 6mm thick foam so I can be protected in the suit, but if it is for props, I would normally use thinner foam, maybe even cardboard.
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