Coleman developed a process to make a plastic liner for coolers and jugs. Thermoelectric coolers Some modern coolers are thermoelectric, plugging into a car's cigarette lighter socket. Rather than using a compressor and refrigerant such as a refrigerator or other heat pump, these use the Peltier effect along with an external fan to draw away the heat. By reversing the current, this concept can also heat the contents instead of cooling them, useful for keeping meals hot from a drive-through, or even to keep items from freezing in severely cold climates. Thermoelectric coolers typically can drop the temperature by about 40 °F or 22 °C below ambient temperature, or can raise it by at least that much; this is really a function of the effectiveness of the boxes' thermal insulation. Some better units even have digital thermostat controls. They do draw a significant amount of power, however, and can drain a non running car's battery so much so that it cannot start. Most electric coolers have an undervoltage shutoff at around 10 or 10.5 volts to prevent this. Many come with power adapters, which use an electronic transformer to convert AC mains or line voltage down to 12 volts, with a lighter-like socket for the cooler's cord to plug in. Some also have a crossover-connection device to reverse the current for heating service. Rotationally molded coolers Rotationally molded (roto-molded) coolers have become popular in recent years. Roto-molded coolers are manufactured using a process called rotational molding, a process by which a heated and softened material is applied to the inner wall of a slowly rotating mold. The mold continues to rotate during the cooling phase, producing a thick and uniform final product. In the case of roto-molded coolers, the heated liquid plastic is applied over a thick layer of insulation. The resulting product has no seals or imperfections and is much stronger and more durable than traditional coolers. Examples of roto-molded coolers include YETI, ORCA or Grizzly coolers. Ride-on coolers A ride-on cooler is a means of transportation that can store and cool beverages and other food products. It is a combination of a low power engine with a go-cart frame which uses the cooler as a seat. The ride-on cooler has the ability to transport food and drinks short distances and can be used in a small backyard, a neighborhood, or at large outdoor parties. The ride-on cooler can