External Frame Backpacks are backpacks that utilize a frame that is visible outside of the backpack as opposed to an internal frame back that utilizes a frame that is built on the inside of the pack and not visible. External frame backpacks are designed to carry heavy loads and keep them stable while transferring the weight of the load to the hips and the hip belt off of the shoulders. The external frame backpack has been used throughout history and until recently would have been made of wood or other natural materials. Since the middle of the last century they have usually been made of lightweight materials such as aluminum.
Today most backpacks are internal frame backpacks, although some manufacturers still make external frame backpacks.