Does anyone know of any plastics that are safe for reptiles in a heated enclosure?

Specifically ones that can be cast/poured. I am no longer able to find the hides I was using for certain sizes of snakes so I want to make some of my own. I have access to jewlery/casting equipment and experience with them through my grandfather who is a jewler. If I can find a apporiate plastic(safe) then I'll make a mold of a hide and just cast several for myself.

Any information would be greatly appreciated.

Sean.
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1.1 BRB
1.1 Triple Het TPRS's
0.1 Silver TPRS
1.1 Amel Bloodred Corns
0.1 Abbott Okeetee Corn
0.1 Blizzard Bloodred Corn
1.1 Thayeri Kingsnakes
0.1 Reeve's Turtle
0.2 Amstaff's
1.0 Pudytat