I have a question regarding the use of certain tapes when it comes to duct seams/fitting connections. Looking at code books, they state UL-181A tape is to be used for all joint connections. Does this tape have to have mastic/butyl? Because there are UL-181A rated tapes that are just foil backed tape. I'm sure it will come down to "whatever your local inspector says," but if the tape is UL-181A, I personally think the mastic/butyl portion does not matter. Just looking for general opinions out there.