Flat Poly Bag 3X18 4 mil 1000/CTN. These Prism Pak Brand bags are made of 100% virgin Low-Density Polyethylene (LDPE) resin that meets FDA/USDA specifications. Prism Pak Brand bags can hold everything from small parts to all types of food items. They can also be heat-sealed to provide security and/or retain freshness. Prism Pak Brand bags are in stock and usually ship within 24 hours.