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Two divers, one wearing a 1 atmosphere diving suit and the other standard diving dress, preparing to explore the wreck of the RMS Lusitania, 1935

A diving suit is a garment or device designed to protect a diver from the underwater environment. Modern diving suits can be divided into two kinds:

• "soft" or ambient pressure diving suits - examples are wetsuits, dry suits, semi-dry suits and dive skins
• "hard" or atmospheric pressure diving suits - an armored suit that permits a diver to remain at atmospheric pressure whilst operating at depth where the water pressure is high. Main article: atmospheric diving suits.

There are five main types of ambient pressure diving suits:

• wetsuits
• drysuits
• semi-dry suits
• dive skins
• hot water suits

Apart from hot water suits, these types of suit are not exclusively used by divers but are often used for thermal protection by people engaged in other water sports activities such as surfing, sailing, powerboating, windsurfing, kite surfing, waterskiing, caving and swimming.

Ambient pressure suits are a form of exposure protection protecting the wearer from the cold. They also provide some defence from abrasive and sharp objects as well as potentially harmful underwater life. They do not protect divers from the pressure of the surrounding water or resulting barotrauma and decompression sickness.

The suits are often made from Neoprene, heavy-duty fabric coated with rubber, or PVC.

Added buoyancy, created by the volume of the suit, is a side effect of diving suits. Sometimes a weightbelt must be worn to counteract this buoyancy. Some drysuits have controls allowing the suit to be inflated to reduce "squeeze" caused by increasing pressure; they also have vents allowing the excess air to be removed from the suit on ascent.

Standard diving dress, a sixth type of ambient pressure diving suit, is now obsolete but is historically interesting.

Main article: wetsuit

Wetsuits are relatively inexpensive, simple, Neoprene suits that are typically used where the water temperature is between 10 and 25 °C (50 to 80 °F). The foamed neoprene of the suit thermally insulates the wearer. Although water can enter the suit, a tight fitting suit prevents excessive heat loss because little of the water warmed inside the suit escapes from the suit.

Main article: dry suit

Drysuits are used typically where the water temperature is between -2 and 15 °C (28 to 60 °F). Water is prevented from entering the suit by seals at the neck and wrists; also, the means of getting the suit on and off (typically a zipper) is waterproof. The suit insulates the wearer in one of two main ways: by maintaining pockets of air between the body and the cold water in standard air-containing fabric undergarments beneath the suit (in exactly the way that insulation garments work in air) or via (additional) foamed-neoprene material which contains insulative air, which may be incorporated into the outside of the drysuit itself. These mechanisms work in tandem; drysuits without neoprene foam require more undergarments.

Semi-dry suits are used typically where the water temperature is between 10 and 20 °C (50 to 70 °F). They are effectively a thick wetsuit with better-than-usual seals at wrist, neck and ankles.

The seals limit the volume of water entering and leaving the suit. The wearer gets wet in a semi-dry suit but the water that enters is soon warmed up and does not leave the suit readily, so the wearer remains warm. The trapped layer of water does not add to the suit's insulating ability. Any residual water circulation past the seals still causes heat loss. But semi-dry suits are cheap and simple compared to dry suits. They are made from thick Neoprene, which provides good thermal protection. They lose buoyancy and thermal protection as the trapped gas bubbles in the Neoprene compress at depth. Semi-dry suits can come in various configurations including a single piece or two pieces, made of 'long johns' and a separate 'jacket'. Semi dry suits do not usually include boots, so a separate pair of insulating boots are worn.

Dive skins are used when diving in water temperatures above 25 °C, 77 °F. They are made from Spandex and provide little thermal protection, but protect the skin from stings, abrasion and sunburn. This kind of suit is also known as a 'Stinger Suit'.

Hot water suits are used in cold water commercial surface supplied diving. An insulated pipe in the umbilical line, which links the diver to the surface support, carries the hot water down to the suit. The diver controls the flow rate of the water from a valve near the diver's waist. Pipes inside the suit transport the water to the limbs, front of the torso and back of the torso.

• Some divers wear a wetsuit under a membrane drysuit.
• Some divers wear a thin "shorty" wetsuit under a full wetsuit.
• Some divers wear a "skins" under a wetsuit. This practice started with divers (of both sexes) wearing women's body tights under a wetsuit to get a bit of extra warmth.

U.S. Navy diving dress being lowered into the water

• Timeline of underwater technology
• Space suit
• Standard diving dress
• Atmospheric diving suit
• Wetsuit Guide

• Experimental Dive Suit Flies Navy Divers Where None Have Gone Before - Development of a 1-atmosphere diving suit.
• Scuba America Historical Center - The development of the first wetsuit.
• LA Times: Surfing whodunit - The history of the wetsuit.