Mineral stone wool insulation batts are slightly better insulators than the off-the-shelf fiberglass batts sold at most lumberyards and home centers. Mineral wool batts for 2×4 walls have an R ...

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.