We insulated the exterior walls with 2″ of closed cell spray foam on the bottom 3 foot, and with 3.5″ of open cell spray foam in the rest of the cavity. We shaved the foam and cleaned the studs as needed to allow for finishing. Spray foam provides excellent insulation and weatherproofing for metal buildings. It forms an integral bond with metal building surfaces and conforms to irregular surfaces to provide an effective air seal.