Refrigerated lunch bags are designed with a layer of gel inside the fabric that keeps the food inside cool. Depending on the bag, the removable interior lining of the bag or the entire bag needs to be stored in the freezer overnight to cool the gel down. The outer layer of the bag is insulated to prevent too much of a loss in the temperature. Those bags are usually made of fabric as the gel makes the outer bag more prone to condensation.
Lunch bags are manufactured in a variety of styles to appeal to a large number of customers. They can be fabric and sport a unicorn for little girls or be leather with embroidery for the professional segment of the market. Prices rise with the complexity of the design and the materials used in its fabrication.
Lunch bags, beside their first function of transport, can be designed to keep food at a certain temperature. All but the cheapest of lunch bags have a layer of insulation embedded inside the bag. That layer is design to keep the heat inside the bag in the case of hot food or outside the bag in case of cold food. The insulation layer is usually made of heat-reflecting material similar to aluminum that is layered between the interior and exterior fabric of the bag.
Lunch bags can use metal in their fabrication. Metal containers are made of aluminum, they can be insulated or refrigerated and usually are richly decorated. The decoration they sport is usually a well-known fictional or real character. Tin Totes are highly collectible lunch boxes and can appeal to a wide age range of users.