The internal frame backpack is a recent creation, invented in 1967 by Greg Lowe. An internal-frame pack has a large fabric part around an internal frame. The frame is made with strips of aluminum, titanium or plastic. A number of straps work with the frame to balance the weight and hold it in place. The internal frame lets the pack fit closely to the wearer's back, which is good when the wearer is doing something that involves upper-body movement. However, the tight fit makes it hard for the skin to breathe, so the user's back often becomes sweaty. The internal design also makes a large storage compartment. Lash points are few, and since the frame is integrated, it is hard to securely attach larger and heavier items to the outside. Internal frame packs originally had smaller load carrying ability and less comfortable fit during walking, but 21st century ones are better. In addition, because of their fit, the better internal frame models have replaced external frame backpacks for many activities.