What is your project? Do you have an existing cat house or do you want to build one?
Generally speaking Styrofoam is an excellent insulator.
a large plastics tote with lid, cut a circle out of the lid so cats can into the tote, pad the bottom of the tote with straw.
Here's a short video:
In addition, use Mylar sheets as they will reflect the cat’s body heat back to them.