What is the difference between a box body and a refrigerated trailer?

A refrigerated trailer is a box body with insulated wall panels and an external active cooling unit that holds cargo temperatures from +12°C down to -25°C throughout transit. A dry box body has no insulation layer and no cooling equipment. The reefer's insulation panels reduce internal usable width and height by approximately 80 to 120 mm per wall face compared to a dry box body of the same external frame size, cutting usable load volume by 15 to 25 percent relative to an equivalent uninsulated body.