Abstract: Folding doors of the type commonly used as garage doors have to date had very unsatisfactory thermal insulation characteristics. The folding door of the present invention has improved thermal insulation characteristics derived from the use of a thermal insulating panel which comprises a body of plastics material having a series of closely adjacent passages extending transversely between opposite edges thereof. The passages are air filled and are isolated from one another over the full width of the insulating panel. Opposite ends of the passages are closed by closure means at opposite side edges of the panels so as to form a plurality of totally enclosed pockets extending horizontally of the door and thereby provide panels having high thermal insulation ratings.