Steel entry doors are the ideal choice if you’re looking for strength and durability. Comprised of a wood or steel frame filled with high-density foam insulation, steel doors are covered with a steel skin (usually 24-gauge, though the skin can be thicker on higher-end doors). Standard doors are coated with a baked-on polyester finish, while more expensive doors often have a vinyl coating for superior weather resistance. The downside to steel doors is that they have to be painted periodically, and they are less energy-efficient than wood or fiberglass doors because they conduct outside heat and cold to the inside.