Overhead Bunk Insulation Board

[Nadine]

I had water damage in my Winnebago Itasca Spirit 2000, model 24v overhead bunk. What I found, in the front of the bed was some sandwich looking board. It had plywood then Styrofoam the plywood and contact looking paper. All toll it was an inch thick.

What is that board called and where can I buy it? I live in PA.

Thanks for any suggestions
Nadine