My company is currently working on a largish job putting in 8 new rooftops with all new ductwork. Under normal circumstances we always seal the duct with most normally a mastic style product. On this particular job the office failed to inform us workers that it was absolutely necessary to do so; so our immediate boss said don't worry about it. Opps. Turns out our inspector is a stickler for the rules, and after having already taped all of our insulation seams, we now have to go back and cut open everything in order to seal the duct seams. So after you read all that, here's where the question begins. The inspector is insistent that we use ul-181 rated tape. It is what is referenced in the IMC book that he goes by and will not accept anything else. We only found this out after having already taped a few seams with ul-723 rated tape, which has the same rating of the mastic product that we use on all of our energy star and LEED projects. Does anyone have any information or knowledge about the differences between these two tapes, which is better or worse, etc. Any info would be appreciated.