Nashua Foilmastic Tape acts as a superior closure and sealing system for use with UL listed flexible, non-metallic air ducts and air connectors. Permanent air tight seal on sheet metal ducts. Sheet metal repairs. Passes SMACNA 1/2 in., 1 in., 1 in., 4 in., 6 in. and 10 in. w.g. pressure classes and seal classes A, B and C (results confirmed by the SMACNA Research and Testing Institute) for use on rigid sheet metal HVAC systems.