4lb Foam

4lb foam, #4 foam, and puzzle mat all refer to a type of durable closed-cell foam often used for the initial box on a weapon. The "4lb" refers to the weight of the foam per cubic foot. It is an EVA foam (which also comes in the 2lb variety- often used for the outer layers of a weapon).

Fine celled foam may require more dap that large-celled polyethaline, so don't be skimpy with the dap, and possibly put on a second coat.

Foametheus

wesellmats

Walmart