Abstract: A folding door for industrial use utilizes a curtain having a series of spaced-apart panel sections which are insulated, and one or more folding hinge sections spanning adjacent panel sections. The hinge sections are generally made of flexible sheet material thinner than the insulated panel sections. Such a curtain is suspended from a doorway, and is opened and closed by folding and unfolding the curtain around the hinge sections. The folding door of the invention is particularly advantageous for use in large industrial refrigerators and freezers.