Nasco Whirl-Pak® Sterile Sample Bags are made of high-quality blended polyethylene. Leakproof closure (whirling or tightly folding the tab over 3 times) prevents impurities from entering the bag and contaminating the sample. Bags are sterilized using ethylene oxide gas at an independent ISO-certified facility. FDA approved. Capacity is measured in fluid ounces. Volume and dimensions are approximate. Whirl-Pak bags are 2.25 mil (.057 mm) thick. Bags should not be used at temperatures above 180° F (82° C).