Types of fins have evolved to address the unique requirements of each community using them. Scuba divers, in particular, need large wide fins to overcome the water resistance caused by their diving equipment; snorkelers need lightweight flexible fins; ocean swimmers, bodysurfers, and lifeguards favor smaller designs that stay on their feet when moving through large surf and that make walking on the beach less awkward. In general there are two main groups of fins; full foot and open heel. Full foot fins fit like a shoe, and are designed to be worn over bare feet. If a larger size is chosen, however, full-foot fins can also be worn over socks and thin-soled booties. They are commonly used for surface swimming, and are in non adjustable sizes. Open heel have a foot pocket with an open heel area, and the fin is held to the foot by springs or straps. They can be worn over boots, and are common in diving. Many companies design fins with the same fin architecture but a choice of heel type.