After a little research, yes they are both polyurethane-based insulating foam sealants and just remember you want to cover the foam with a 100 percent silicone layer to put your substrate into.

The CERESIT WINTER TS51 foam shows it is non-toxic after curing.
I would do some test strays to see how much it expands and how easy it is to carve once it dries before doing your background with it.


As for Eggcrate. It is a lighting louver or light fixture cover and that is where you'll find it in most hardware type stores.
Take a picture of it with you..... you can find a picture of it here: http://i00.i.aliimg.com/photo/v0/206...ers_grille.jpg