I just cut pieces of this to make bottoms and covers for many of my 15/32" thick nucs -->
This is 2" thick polystyrene, it's easy to cut with any sharp knife and a straight-edge. I use canvas, old towels, or pieces of plastic trash can liners as inner covers, and #8 hardware cloth to cover the poly bottoms, this keeps the bees from nibbling away the poly. The plastic film covering both surfaces can be peeled away so it can then be painted where exposed to sunlight (over time sunlight will weaken it, unless painted). It helps keep hives cool in Summer and warm in Winter.
I've never had the slightest bit of warping when using polystyrene this way. When the plastic film is peeled away it can also be glued together with polyurethane glue - like gorilla glue, making custom configurations like telescoping outer covers.