To provide lab data about which sealants and tapes last, and which are likely to fail, we are conducting ongoing accelerated testing at Lawrence Berkeley National Laboratory Environmental Energy Technologies Division. Our major conclusion so far is that you should use anything but duct tape to seal ducts. The testing we've done so far shows that under challenging but realistic conditions, duct tapes fail. A report of of our research in Home Energy magazine provides more information on the longevity and failure rates of various duct sealing methods. All the other tapes we tested that claimed to be useful on ducts passed our test.
Tapes require a clean, smooth, dry set of surfaces to hold well.
Non-tape sealant approaches such as the use of mastics may perform better. Aeroseal Inc. of Austin, Texas is working to commercialize this technology.