These vacuum-sealer pouches, 8-inch by 12-inch, from VacMaster (model 30754) are extra thick and tough, four millimeters in thickness while standard pouches are 3mm. Like all VacMaster's fine vacuum bags they're composed of transparent nylon/polyethylene, glossy and transparent. Being 4- millimeters thick they are designed to be especially puncture-resistant and so are the ideal choice for sealing boney, sharp-cornered or spiney items, items that might puncture a 3-mil bag. Once sealed, bags may safely be microwaved or heated in a sous vide basin; you can also boil them (for as long 20 minutes. Package of 1000. Designed to take a tight seal in vacuum sealers of the chamber type (these bags probably won't work in a suction or external vacuum sealer. B.P.A.-free. Bags are F.D.A. approved. Vacuum sealing prevents spoilage and freezer burn, keeps food items fresh and edible for long periods (up to five times the duration of comparable means of storage.