The frame of an external frame pack is made from aluminum or other light material. It also has straps and a stretched netting which keeps the metal frame off the user's back. External frame packs have a fabric "sack" part which is usually smaller than the sack of internal frame packs. Nevertheless, they have exposed frame portions above and below the sack to make it easier to hold larger items. In addition, the sack can often be removed entirely. This lets the user change the arrangement of his load, or to move an unusual load. Military packs are often external frame designs because they can carry loads of different shapes, sizes and weights.