What's the Difference: Duct Tape
Polypropylene vs. Butyl
The best way to seal most duct seams is with mastic. However, some duct seams call for an easier-to-apply sealing method: tape. There are a great many types of duct-sealing tape, made with a variety of adhesives and backings, but the two most durable types are oriented polypropylene duct tape and butyl duct tape.
Ordinary rubber-adhesive duct tape may be great for a lot of tasks, but sealing ducts isn’t one of them. This tape dries out quickly and can peel off metal ductwork.
Before choosing a tape, consider that building codes require duct tapes to carry a UL 181 label, though in many areas of the country, this is not enforced. Also, according to tests performed by researchers Iain Walker and Max Sherman at Lawrence Berkeley National Laboratory, a UL 181 listing is no guarantee that a tape will last any longer than unlisted duct tape.
For repairing the outer…