Level I
An economical, non-insulated, single steel skin door.
Level II
Single steel skin construction with polystyrene insulation, covered with white vinyl backing. (R=6)
Level III
Sandwich steel construction uses two steel skins laminated to a polystyrene core for added strength and a higher insulation value. (R=9.65)
Level IV
High R-Value (R = 17.54) urethane core doors.