We use spray foam insulation because it adheres to the surface of the vehicle and adds to the overall integrity. Spray foam is moisture resistant and does not shift and fall inside the walls like bat insulation. Our spray foam insulation has an R-rating of 7 per inch. The R-value is a measure of thermal resistance used in the building and construction industry. It is the ratio of the temperature difference across an insulator and the heat flux (heat flow per unit area). Higher R-ratings translate to better insulation.