Made from 5 mil thick FEP fluoropolymer film. These flexible, sturdy bags are heat sealed on all four sides for complete chemical resistance and leak proof operation. Inert to almost all chemicals. Low permeability of FEP limits sample loss. Feature a nickel-plated, brass on/off valve that accepts 1/4"I.D. flexible tubing or with PTFE/silicone septum in polypropylene housing for use with a hypodermic needle. Easy to use. Unlimited storage life prior to use. Can be used for gas sample analysis, extracting air samples from smokestack exhaust systems, monitoring air quality or calibrating instruments in the field. Individually packaged.