In recent years, twin doors (or cabinet doors) have been less popular
than the bi-fold door alternative.
The term "Twin Door" refers to doors which each swing out
like kitchen cabinet doors during opening the doors. This means that
there are only two pieces of glass.Some recent styles even fold flat against the fireplace brickwork after they are fully open. The two constructions are virtually identical, but the highes for the Full-Fold versions are very slightly farther out toward the room, to allow the full swing of the doors.
Closed, this looks exactly the same as the other version.
JDoor's
Fireplace Door Selector Page is at:
http://mb-soft.com/juca/info/doors/firedoor.html