A Door Jamb (or Door Frame) is what holds a door in place. Most residential doors have wooden door frames. Most commercial buildings have steel jambs. A door with a steel jamb will likely cost $1,000 or more and is much more difficult to install. Many people think that steel doors have steel frames. For homes, that is rarely the case. Many homes have door slabs that have a steel exterior. While these doors are more secure, wooden frames break easily and "steel" residential doors are doors are actually made of foam and are covered by 24-gauge steel skin. The only solid part of most steel doors is a 12-inch wood block in the lock area. This is why steel doors will often split if not reinforced.