No idea about the material but flexwatt can heat through 1/2" easily. My AP cages use 1/2 PVC and I use flexwatt for all of them and it works just fine.
Yah, I can imagine plastic conducts the heat quite well. Im just less sure if it will make its way through melamine or other wood products
1.0 Albino het red axanthic
0.1 Albino spider
0.1 American Bulldog