A wetsuit provides divers and surfers with protection from cold and abrasions. They also provide additional buoyancy in the water, especially at greater depths. They're relatively light-weight and allow an adequate range of motion while still remaining snug enough for good insulation and comfort. The cut and thickness of the suit depends on water conditions and the wearer's purpose. Here are some basics about wetsuits to get you acquainted.
Wetsuits are traditionally constructed from neoprene foam that traps tiny nitrogen gas bubbles under it's surface. This is the main basis for the insular and buoyant effect of wetsuits; the other contributing factors in hypothermia protection are fit and thickness. Though they were originally made of only neoprene, backing was necessary to prevent damage to the fragile material.
Modern wetsuits are constructed of a neoprene core between layers of either nylon or spandex. Wetsuits range from 2mm rash guards that are similar to T-shirts to 8mm full-body suits that can be semi-dry also. A semi dry suit is one that's constructed to allow minimal amount of water exchange; insulation is provided primarily by the thickness of the material. Optional hoods, boots and gloves are available for frigid conditions.
A wetsuit should be just snug enough for comfort, with enough room between the suit and the body to allow a thin layer of water to fill the suit. This helps retain body heat and adds another layer of insulation. The wetsuit should also allow a good range of motion without adding bulk or folds. The neck and cuffs of a wetsuit should be reinforced and flexible to prevent water and heat loss.
Wetsuit styles varying according to climate and need. The smallest are thin, one-layer garments with a raised neckline and short sleeves; they cover only the torso and abdomen. Divers should wear at least a full-length, medium thickness suit even in fairly moderate water if they will be submerged for a long time. Even in warmer waters, there's and increased danger of exposure the longer you're in the water. This not only protects from the cold, it also protects against damage from scraping against underwater rocks and coral.
Professionals divers and athletes who experience a variety of conditions and dive year round would do well to invest in several wetsuits of varying cuts and thicknesses. Another alternative is to buy a convertible suit that has detachable arms and legs.