FOIL-GRIP 1402 Mastic Duct Sealant 2 X 100'

Seals ductwork well, you will never get the ductwork apart. Thick glue with a good seal. Top notch.

Great price for how much you get. Very sticky. Easy to use. I use on my hvac registers after cleaning them up. Keeps attic air out. Seems like quality product. Very strong. Does its job by making an airtight seal.

There's no better tape period, this is the real deal. Quality product, pricy, but worth every penny. I had multiple air bleed connecting seams, did my entire basement ductwork with 100 feet and some left over to do a few more seams. Get some little scissors to cut it with, makes life easier. The utility blade crumples the corners a bit, which makes it trickier to get the backing off. Hope this helps!

So, I like using heavy mastic and a brush. I have quite a bit of ductwork in the attic to strip and mastic. The problem being, after brushing on mastic, I can't run the AC until it dries, basically by the next day. Well it was 100° here the other day. It hit 140° in my attic: measured, not estimated. Welcome to spring where I live. Basically that's 2 days of not running the AC to mastic ducts. Rough. Then it occurred to me. I had already ordered this mastic tape but hadn't been using it. I can mastic tape the seams, then go downstairs and run the AC. This has been life cha... ok, maybe not. But it has given me options I hadn't realized I had before. I don't have to check the weather reports and pray for a string of cool days in order to seal my ducts and not fry for 2 days for each section I do. The tape sticks very well. If it didn't, no one would buy it. Free the edge of the backing from the tape, measure out the tape against where you want to put it, and notch the edge with a razor blade. Peel the tape from the backing past the notch, then cut the tape where the notch is. Don't cut the backing! Eventually you'll end up with a long strip of backing. Trim it off, but Not even with the end of the tape. You always want some backing there past the end of the tape. The other way lies madness. You do not want to be in the dark attic, sweating, cursing, trying to get a corner of the tape started off the backing. I expect I'll need more of this tape. I'll still use buckets of mastic where necessary like on register boxes where I can't always reach where I need to get with tape, but this mastic tape has made it more convenient for me.

This stuff is great! Seems good, flexible to get around uneven surfaces and mold to it/hold tight. Way better than the crappy little foil tape you get and the big box store.