Styrofoam Ag Board from Dow is an extruded polystyrene insulation board with ship-lapped edges that help reduce heat loss and gain. It can be left exposed on the ceiling and walls of buildings not occupied by humans. Its closed-cell structure leaves no voids or gaps for water penetration, thus providing high moisture resistance. It is available in a wide range of thicknesses and lengths, is lightweight and easy to cut, can be pressure-washed at 800 psi and comes with a 15-year thermal warranty.