Foam for Insulation, not structure

What types of foam can I use to insulate fish boxes? they will be constructed of ply under glass, but I will need to lay up a foam layer. I cannot use expanding foam, since thee is no dead space for it and the faom needs to be flat to lay glass over.

 

Even a little help would work.

 

cut and fitted styrofoam.
Free, easy.
But then of course there would be many other options as well.

 

Regular styrofoam will melt after the appliocation of polyester resin. The Pink insulation foam fro Hoem Depot will also melt. I need something that will not melt. But thanks for the reply......

 

You need the polyurethane stuff from Home Depot which is brown colored and covered with foil or you can go to an insulation supply company and get some polyisocyanurate foam that is used on roofs, usually commercially. The polyiso comes in different thickness's and is somewhat structural as they have to make it tough enough to walk on. I've made 4x4x4' fishboxes with just it and no ply. Cut to shape and either pin together with wire or nails or tape with metalic foil tape like used in AC ductwork and then glass. Sam

 

Or use epoxy over styrofoam