The secret is freezable gel built right into the walls of the bag. To use, simply flatten the bag and place the entire bag in the freezer overnight. In the morning, the walls of the Hampton Lunch Bag will be completely frozen and ready to chill food and drinks for hours. Specs Gel-lined walls chill a meal, snack and a 12oz (340ml) drink for hours (depending on external temperatures) Wide rectangular base fits a Mod Lunch Bento™, Mod Snack Bento™, Flex Bento™ containers and bottles Comfortable shoulder straps Zip closure locks in cool, dry air Collapses flat and freezes overnight Reusable, nontoxic and food safe Made from nontoxic poly canvas;food-safe lining PVC-, BPA-, phthalate- and lead-free Interior wipes clean; spot clean exterior Proudly made by PackIt: creator of the ORIGINAL foldable, freezable lunch bag. Designed in California