Cooler Bag Technology
The original ice chest was made out of galvanized metal. Later versions were made from hard plastic. They were double-walled with a layer of dense Styrofoam in between which helped to keep the contents cool. Today’s ice chests are still made this same basic way.
Styrofoam was a suitable insulator, but it had to be relatively thick to maintain internal temperatures for an extended period of time. And, of course, Styrofoam is easily dented and broken, so it had to be encapsulated in a hard shell to prevent breakage. As such, ice chests have to be rigid.
By contrast, cooler bags are not rigid. Instead, they are usually made from heavy but flexible fabrics, like polyester, on the outside. The inside is lined with heavy duty foil. In between the outer and inner layers are layers of materials like flexible foam, which are thin but dense and have the ability to maintain internal temperatures for several hours. This technology allows for a bag that is flexible and thin and, therefore, easy and convenient to transport. Also, unlike their rigid predecessors, cooler bags can be manufactured in a wider variety of sizes and shapes.