Yeah I was wondering that when I saw the video clip. You could always try using a snug fitting bike helmet if you do another, take off the plastic outer shell and trim down the top and sides to use as a base. I used to do stuff like this for friends and I found it was a good way to make a generic size cosplay helmet. Because of the polystyrene most helmets use you have to be careful when using other chemicals like resins on them though as they could just melt the helmet base. It's a great material to use though and the bike helmet doubles as the perfect way to keep the helmet/mask on and straight. Polystyrene is a great material to use though if you start with even a helmet and get another sheet of it to cut into shape, then I found the best option was to bend out paperclips to stick through the meeting edges to hold the pieces together to get just right and then use (my preferred method) hot glue to seal the edges. You have to use a TON of paint and resin though to get that smooth texture, and it's a lot of work between resin and sanding layers, but the quality in the end is nearly movie prop level. If you get really brave down the line, bondo and fiberglass.