Proper air-sealing is one of the keys to an energy-efficient house, but choosing the right air-sealing tape can be a challenge. In this article, senior editor Martin Holladay writes about his informal backyard test of 11 air-sealing tapes. Holladay attached several substrates to his shed, then applied strips of various tapes to see how they held up over the course of a late-fall month. The tapes use three types of adhesive: rubberized asphalt, butyl, or acrylic. The 11 tapes spanned a wide price range and included products from Dow, Venture, Nashua, Siga, Zip System, Polyken, 3M, and Pro Clima. The substrates included XPS, foil-faced polyiso, plywood, OSB, housewrap, and polyethylene. In the end, Holladay learned that there is no such thing as all-purpose tape and that certain tapes work better with specific substrates. This article includes sidebars about the economics of choosing tapes and substrates, and about the issue of vapor permeance.