Soot Ash Vacuum Vac Bag Master Craft 605 641 1100 6500 S12 3-1/2 gal 5-Pack
When soot's involved, the seam matters. When bags inflate, the entire force is put on the seam holding the bag together. Other bags rely on a glued lap seam that can give way under pressure.
Westwood's seam is on the edge, which gives a stronger, wrap around seal