Thermal insulation for hide box???

[Pythline08]

Hey everyone at the moment im building a hide box for my diamond for his outdoor enclosure.. the hide box is a fully enclosed box with one entry hole at the front i want to line it with a material to help assist with thermal warming/insulation when we have some of those random cold nights. I was thinking about styrofoam?? what do people think about that idea, any other suggestions???

Cheers