Polyurethane closed cell spray foam is the most efficient container home/storage insulation solution. It will offer the highest insulation value at approximately R-1 Per inch. Spray foam completely covers the surface of the corrugated shipping container walls leaving no gaps between the insulation and the container walls. There is no better moisture/vapour barrier than closed cell spray foam insulation. Do it once and do it right use closed cell spray foam insulation on your container modification!