External frame packs were designed to carry heavy loads (>20 kg or 40 lb), giving the wearer more support and protection and better weight distribution than a simple, frameless strapped bag. Wooden pack frames were used for centuries around the world. Ötzi the Iceman may have used one in Copper Age Alpine Italy,[5][6] though some archaeologists believe the frame found with the body was part of a snowshoe. Such packs are common in military and mountaineering applications;[7] metal versions first appeared in the mid-20th century. https://i.pinimg.com/originals/b6/65/1c/b6651c43980c094ae096da3fe3fe7e49.jpg

The external frame is typically made from aluminum, other lightweight metal alloy, and recently reinforced synthetic polymers or plastic and is equipped with a system of straps and tautly-stretched netting which prevents contact between the metal frame and user's back. In addition to comfort, this "stand-off" provides the additional benefit of creating air circulation between the frame and the wearer's back. For this reason, external frame packs are generally considered to be a "cooler load" than internal frame designs. External frame packs have a fabric "sack" portion which is usually smaller than that of internal frame packs, but have exposed frame portions above and below the sack to accommodate attachment of larger items. In addition, the sack can often be removed entirely, permitting the user to customize the configuration of their load, or to transport a non-conventional load such as a quartered game animal. Military packs are often external frame designs due to their ability to carry loads of different shapes, sizes and weights. https://i.pinimg.com/originals/b6/47/96/b64796a90bd0726ae5fa1a8a7f2ae250.jpg
A daypack is a smaller, frameless backpack that can hold enough contents for a day hike, or a day's worth of other activities. They are not large enough for average wilderness backpacking that use full-sized sleeping bags and backpacking tents, but may be large enough for ultralight backpacking. Padded or unpadded waist straps may be provided to distribute weight across the body. https://i.pinimg.com/originals/71/06/b5/7106b5222162bcb9bc6e8f7bbaf2d0f0.jpg