The way Burns made the original masks was by taking lifecasts and then building the mask with layers of liquid latex with fiberglass insulation in it. As far as I’m aware the original insulation hasn’t been made in very many years, but something similar is this yellow pipe wrap insulation. You need to take a pair of gloves and very carefully split it off into thin layers. It should be like tissue paper.
It’s easier to work into a negative mold (meaning you lifecast someone, clay press it (pour hot clay in to produce a positive sculpture) then make a plaster mold of that clay sculpture (ultracal, hydrocal, pottery plaster) to make your mask in.
You CAN make it over a positive cast (meaning lifecast, then make a direct plaster copy, or buy a premade plaster lifecast from eBay. The only issue is you will lose surface detail and the surface will inevitably end up lumpy. Which is fine depending on how “decayed” you want the mask to be.
So once you have your mold, or your plaster lifecast, and thin layers of insulation, it’s very simple. Brush one very thin layer of liquid latex. Let that dry. Once it is dry, brush in another very thin layer and then start laying in your fiberglass insulation. Once again, you will let this dry. Then you go in with a coat of latex only, to fully saturate the fiberglass insulation you put in. This one will take longer to dry, put it in front of a fan and leave it alone until it is completely bone dry. Finally, go in with one final layer to seal any remaining fiberglass insulation. It should be sealed 100% under a layer of rubber on the front and back. You do NOT want any contact between the insulation and the actors face, if this is planned to be worn.
If all goes well, you should have a very nice leatherface style mask. You can carefully stretch and distort it, and due to the fiberglass inside it will hold that shape. Wherever you cut the mask, I like to go in with more latex on a brush and seal everything closed, once again to make sure absolutely no fiberglass will come in to contact with skin.
