Abstract: In a very high or very low temperature duct system in which duct insulation is terminated at selected locations so as to be not coextensive with the duct, an annular metal perforated or mesh screen support flange is used, as a low conductor of heat or cold, between the duct and an outer insulation cover to retain the end of the insulation and to support its usually very thin cover. The screen may be Z-shaped in cross section having a small diameter annular portion to surround and be secured to the duct adjacent the end of the insulation. A generally radially extending portion of the screen extends outwardly from the small diameter portion and adjacent the end of the insulation. The periphery of the radially extending portion is in alignment with the outer peripheral surface of the insulation and the outer peripheral surface of the insulation cover.

Abstract: A lightweight, high-strength duct comprised of two thin annular tubes, one fitted within the other, the outer tube having spaced annular stiffening beads extending radially outwardly therefrom, and one of the tubes being vented to prevent pressure differentials between the inner surface of the outer tube and the outer surface of the inner tube at various altitudes and temperatures.