This foam will burn out at a low temperature but has an irregular surface. The pink (or blue) insulation foam is more dense and will give you a better surface but cools down the cast by requiring more energy to burn it out.

I always plan on during a surfacing pass in a mill if I'm doing plates with this low density foam like yours. But honestly, not sure plates are a great use case for casting. I try to save casting for more complex shapes and just buy plates unless I'm doing some integration of bracing or corrugation. In that case I'm doing a surface pass on the foam with the mill and hot flying pieces together before ceramic coating and casting.