Duct Tape and Sealant Performance

It's in garages, kitchens, cars and boats. Books have been written about it. Wallets made from it are sold online. What is this infinitely useful product? Duct tape, of course. Although it serves so many purposes, it is important to understand how duct tape works for its ostensible purpose—to seal ducts. At the Lawrence Berkeley National Laboratory (LBNL), we have studied the durability and longevity of duct sealants for more than a decade and have created test methods for evaluating these properties. What we found was almost every product intended to be a duct sealant works—except duct tape. In this article, we summarize what we found and describe some of the work we did to evaluate duct tape and other sealants. The project began in the mid-1990s when California utilities were convinced that sealing air leaks in ducts was a cost effective measure for saving energy and ensuring good distribution of air throughout a building. They were concerned by the many anecdotal reports of duct sealant failures in the field and wanted to be able to recommend or require good sealing methods. They approached LBNL about creating a laboratory test method that would rate or rank duct sealants on their durability. We developed a test and expected to see a spectrum of results for different sealant products, but what we found surprised us. We found most types of sealants passed our test without any significant failures. These products included mastics, a wide spectrum of tape products with acrylic or butyl adhesives, and aerosol sealants. The only product class that failed consistently, and often catastrophically, was cloth-backed, rubber-adhesive tape—commonly called duct tape. As with many other building products, duct sealants are rated by Underwriters Laboratory using UL 181B safety standards. These standards are used by many jurisdictions as a requirement for duct sealants. When we began testing, few duct tapes existed that were UL 181B rated, but the ones we tested for sealant durability had similar failure characteristics to unrated tapes. Since that time, we have focused our efforts at improving the test procedures and trying to solve the problem of why duct tape could pass the UL 181B tests and not have sufficient longevity to be used in many field applications. To address this problem, we carried out several additional studies to understand the performance and durability of various duct sealing approaches.