When it comes to insulating a metal building, closed cell spray foam should by your number one choice. Here a few of the main reasons why; Closed cell spray foam is extremely dense and can help reinforce the sheet metal that covers the exterior walls and roof by 275%. This virtually makes it storm proof. Another reason is closed cell is so dense it is waterproof and acts as a highly effective vapor barrier. When dealing with metal walls and roofs, condensation can easily build up on the metal and support rust as well as mold growth. Now aside for those examples the foam works superior when deflecting heat transfer from the sun from entering your building or in the colder months it can hold in heat easily during cold conditions.