The bag is thick and filters the circulating air well. I've used it with a Toro vacuum to remove soiled and compacted attic insulation. The bag was on the ground floor of the house while I was working in the attic. Neither fiberglass nor insulating material entered the bag. The bag becomes heavy and a little unwieldy to maneuver around the house once full. I tried using this with the side fill method but it didn't work due to the low CFM of the vacuum used. Switched to top fill method and it worked great. Would buy again.