It is a polyurathane 4 pound density foam.i get it from a local dealer, and the film company usually pays. It is a bit pricey, a 8 foot by 4 foot by 18 inch block runs about $900 to $1000 dollars. You can get it smaller, and it is very messy. There is a cheaper polyurathane foam , that runs about $300 -$400, it is 2 and half pounds density and softer to work. Foam does not last forever, and hardcoating it, or molding it would be adviseable. Good luck.
I use loop tools with teeth, , a sawzall with spiral wire and a rubber hose to cut out the profile and front views, sanding pads, and files and rasps, knives and saws.Start with the larger tools, work your way down to the detail tools, sand .Good luck!