Fiberglass and steel doors are similarly insulated with polyurethane foam or rock wool. As long as the door does not have a glass insert, insulation values range from R-5 to R-6. Fiberglass and ...

Cover fiberglass insulation with drywall to have a fighting ... (Note that some prefab steel or plastic sheds can't be insulated.) In a pinch, you could also use rigid sheets to insulate a steel ...