A rebreather is a type of breathing apparatus that allows the user to breathe their own air over and over again, recycling the substantially unused oxygen content and unused inert content when present, of each breath. The device absorbs the carbon dioxide of the users exhaled breath to permit the rebreathing of the substantially unused oxygen content. Oxygen is added to replenish the amount metabolized by the user. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment.

There are three types of rebreathers: oxygen, semi-closed circuit, and closed circuit. Oxygen rebreathers carry a cylinder of pure oxygen as the only gas supply, while semi-closed circuit rebreathers use gas mixtures as the gas supply. Closed-circuit rebreathers carry both pure oxygen and mixed gases.

The most popular type of rebreather for recreational diving is the fully closed-circuit breathing loop, often referred to as a CCR. The loop uses counterlungs to store the gas when the user exhales and to supply the gas when they inhale. A scrubber canister is also part of the loop, which contains chemicals to act as a carbon dioxide absorbent. The rebreather set point can be controlled using either manual or automatic systems.

Rebreathers have several advantages over conventional scuba, including better gas efficiency, stealth, and extended range dives. They produce few or no bubbles, so they dont disturb marine life or reveal the divers presence. Recreational rebreathers are electronic rebreathers that enable full automation of safety systems and gas composition, allowing the recreational diver to enjoy longer and more comfortable dives than with a traditional scuba setup.

In summary, a rebreather is a type of breathing apparatus that allows the user to breathe their own air over and over again, recycling the substantially unused oxygen content and unused inert content when present, of each breath. There are three types of rebreathers: oxygen, semi-closed circuit, and closed circuit. The most popular type of rebreather for recreational diving is the fully closed-circuit breathing loop, often referred to as a CCR. Rebreathers have several advantages over conventional scuba, including better gas efficiency, stealth, and extended range dives.