Our 12 x 18 4Mil Flat Poly Bags Each of our Layflat poly bags are made of 100% virgin Low Density Polyethylene (LDPE) resin that meets FDA/USDA specifications. Manufactured with either a durable bottom seal or extra strong side weld for optimal strength. This premium bag features superior clarity for showing the quality of your customer's products. All listed gauges are nominal. Can be heat sealed, tied, stapled or taped shut.