I broke a few finger bones in December and after opting out of surgery (a few tendons were fully free) I ended up making casts myself with Instamorph.

Instamorph is a thermoplastic that becomes fluid at 160F, which is not so hot as to cause burns. You can boil it in water then pull it out with a fork or use a heatgun and mold as needed directly on skin to form immobilization supports. I ended up drilling a few plastic casts for better ventilation and reused the plastic tens of times as swelling decreased without issue. It is biocompatible and nontoxic, good for all sorts of things. We use it for prototyping parts, so I happened to have a good supply of it.

Check it out if you're making casts or other plastic parts yourself, it is very useful stuff and I keep some in my truck's first aid kit now.

Amazon.com: InstaMorph - Moldable Plastic - 12 oz: Arts, Crafts & Sewing