A rebreather is a type of scuba diving equipment that recycles exhaled air, allowing a diver to reuse the gas mixture for breathing. Instead of releasing exhaled air into the environment, a rebreather system filters out the carbon dioxide and adds fresh oxygen and/or other gases to create a breathing mixture that can be recycled. This recycling process makes a rebreather system more efficient in terms of gas usage and can also make diving quieter, as there are no bubbles released from the exhaled air.