Rockwool insulation. Works great, we used it for sound insulation around the replacement of the stack coming down from the second floor.
We used around half of the bag, so the are 5 or 6 batts left. Clean and dry and ready to use.
Same as https://www.homedepot.com/p/ROCKWOOL-Safe-n-Sound-3-in-x-15-1-4-in-x-47-in-Soundproofing-and-Fire-Resistant-Stone-Wool-Insulation-Batt-59-7-sq-ft-RXSS31525/202531875 at Home Depot.