Actually, fabric-based "duct tape" hasn't been allowed for sealing ducts for many years in jurisdictions that have mechanical codes - various performance reasons. A metalic type duct tape meeting certain performance criteria is what should be used now-a-days.<br><br><< Lastly, I've seen ads for "100 mph tape." Does anyone know if it's better, worse or no different than what's available in the hardware store? >><br><br>Depends on what you buy at the hardware store. "Mil-spec" tape is the very heaviest and best. Almost as good are the various ones advertised as "90 mph tape" and "100 mph tape". In the same class as those is "contractor grade" brand name stuff like Scotch from 3M. All cost more than the garden variety "duct tape" and all greatly out-perform the bargain stuff in ALL of my experiences with them. If you've never used name brand duct tape in a non-bargain grade, go get a roll and try it in some demanding situations exposed to the elements - you may be amazed at the performance advantage. I refuse to buy the bargain stuff - it's not in the same league as the "good stuff". Save the bargain stuff for non-critical applications like letting kids/grandkids fabricate imaginative things from cardboard boxes, cans. sticks, etc.<br><br>HTH,<br><br>Tom