A rebreather has two purposes it is to eliminate the carbon dioxide and substitute the consumed oxygen. It is a piece of equipment that enables you to breathe your own air, which produces no bubbles. A rebreather recirculates ex-haled gas for re-use.
There are three types of
Semi closed circuit rebreathers that uses a gas combination as the gas source
Closed circuit rebreathers carry both pure O2 and mixed gas
Oxygen rebreathers carry a tank of pure O2 as the only gas source