When installing interior doors, it can sometimes be difficult to decide between steel doors and fiberglass doors. Steel and fiberglass doors have a number of similar traits, being made up of foam insulation surrounded by an outer skin of fiberglass or steel. Both fiberglass and steel doors are cut to similar lengths, and provide good basic insulation against heat loss.
One difference between steel and fiberglass doors is in the frame. Steel doors are often surrounded by a metal frame, the pieces of which are separated by a thermal break. This reduces heat loss through the frame. Steel doors may be colder to the touch, and also reflect heat from nearby radiators and underfloor heating, so users of the door may have to watch for temperature changes. Steel doors can be painted, and are also less expensive than fiberglass.
Fiberglass is often hung in a wood frame, which can transfer some heat loss through convection. However, fiberglass doors sometimes have a metal strip which allows them to be fitted with magnetic weatherstripping, meaning that heat will he kept inside the room more. Fiberglass must be varnished and stained, leaving doors with a wood-look finish. This can be an advantage, although fiberglass is generally more expensive than steel or wood doors.