aLOKSAK OPSAK Waterproof Storage 12" x 20" Odor Barrier Bags Along with being 100% water/air tight like our ALOKSAK, the O.P.SAK (Odor Proof SAK) is also a 100% odor barrier bag. You can store food undetected to bears and other pests in your campsite by sealing them in the OPSAK. Also, because the OPSAK is FDA approved, you can use it in food preparation and storage.