Abstract: A reinforcing net for use in a reinforcing layer is formed by spacing two parallel spreader yarns under tension and wrapping weft yarns around the two spreader yarns. The reinforcing net can either be affixed to an adhesive coated substrate or coated with adhesive at the intersections of the yarns to bond the net together. The net may be affixed to a plurality of substrates to form a laminate. The net, a ribbon of net with one substrate, and the laminate, may be used in making and reinforcing spirally wound products such as ducts, duct insulation and the like. A number of warp yarns can be included in the reinforcing net to increase its strength. The method of manufacturing the reinforcing net includes the steps of creating tension in the spreader yarns, providing a least one spool for supplying weft yarn, longitudinally advancing the spreader yarns, rotating the spool around the advancing spreader yarns and applying adhesive to the intersections of the yarns.

Abstract: A reinforcing net for use in a reinforcing layer is formed by spacing two parallel spreader yarns under tension and wrapping weft yarns around the two spreader yarns. The reinforcing net can either be affixed to an adhesive coated substrate or coated with adhesive at the intersections of the yarns to bond the net together. The net may be affixed to a plurality of substrates to form a laminate. The net, a ribbon of net with one substrate, and the laminate, may be used in making and reinforcing spirally wound products such as ducts, duct insulation and the like. A number of warp yarns can be included in the reinforcing net to increase its strength. The method of manufacturing the reinforcing net includes the steps of creating tension in the spreader yarns, providing a least one spool for supplying weft yarn, longitudinally advancing the spreader yarns, rotating the spool around the advancing spreader yarns and applying adhesive to the intersections of the yarns.

Abstract: A duct formed from at least one helically wound strip of flexible material and at least one stiffening element. Stiffening element has a ratio of radial height to axial length of greater than 1.0. The stiffening element may be substantially planar.

Abstract: A duct formed from at least one helically wound strip of flexible material and at least one stiffening element. Stiffening element has a ratio of radial height to axial length of greater than 1.0. The stiffening element may be substantially planar.

Abstract: A helically wound conduit formed from a single continuous strip, the strip being formed from alternating first and second strip portions. Second strip portions are more flexible than first strip portions and the conduit as a result has greater flexibility in the sections formed from the second strip. A reinforcing wire may be added to strengthen the conduit.