What type of apparatus recycles a user's exhaled air?

The type of apparatus that recycles a user's exhaled air is the closed-circuit breathing apparatus. This system operates by taking the exhaled air from the user and filtering it to remove carbon dioxide, then replenishing it with oxygen, thus allowing the user to breathe the same air multiple times. The closed circuit is advantageous in environments where air supply is limited and can help extend the duration of the air supply while reducing the weight and size of the apparatus.

In contrast, open-circuit breathing apparatus releases exhaled air into the environment, which does not provide air reuse. A supplied-air respirator (SAR) continuously provides fresh air from a stationary source, making it unnecessary to recycle exhaled air. An air-purifying respirator (APR) filters contaminated ambient air for inhalation without the capability of recycling air and is not designed to provide the same degree of air preservation as a closed-circuit system.