These heavy duty (4.5 mil) are ideal for collecting, transporting and long term storage of evidence. These polyester pouches are boilable, freezable, and microwaveable. They will sustain temperatures from -70-240°F, provide superior barrier performance, and safe use with concentrations of most acids, alkalies, grease, oil, and organic solvents. Heavy duty pouches (4.5 mil) are suitable for collection of evidence and long term storage.