Packs such as backpacks, hip-packs, and messenger-packs are often used to carry loads of various compositions and sizes. Much research has been focused towards designing and manufacturing packs to carry such loads more comfortably. One area of research has concentrated on support systems, which are sometimes referred to as support frames, or simply frames. In general, packs typically are either framed or unframed, meaning they either include a structured support system or do not. Unframed packs are typically constructed from one or more fabrics or similar materials that are sewn together or otherwise formed in the shape of one or more compartments. Because an unframed pack lacks a structural frame, the shape of the pack is largely amorphous and thereby defined by the shape of the pack's compartment(s), as affected by the load (objects carried within the compartment(s)) and/or the user's body upon which the pack is supported.
Framed packs are typically described as having either an internal or external frame. External frames conventionally are formed from metal or other suitable structural supports that are connected to the outside of the pack, typically as an interface between the pack's harness and the pack's storage compartment. Internal frames typically include one or more rigid plastic or metal support members that are housed within a compartment of the pack. With a conventional internal frame, the frame has a rigid construction that defines the shape of the flexible pack, which extends over the frame. An example of a simple internal frame is a rectangular sheet of plastic that is secured within a pack to provide stiffness and support to the pack's compartment. Some versions of such packs utilize a flexible plastic material, although the generally rectangular dimensions of the sheet of plastic typically only provide one degree of conformity, such as about the long axis of a user's back.