Below is a list of Closed Cell Foam manufacturers from Boothbay, Maine. Closed cell foam is a plastic that contains foam cells which are sealed, or “closed” and packed together. This foam is very dense and has high compressive strength. Because the cells are not broken in this foam and gas and liquid molecules do not freely travel from cell to cell, when exposed to heated gas the cells expand, filling the material and making closed cell foam an excellent heat insulator.