Most oxygen rebreathers use a simple single counter lung.
Materials used in the early days are finely-woven fabrics, impregnated with
rubber or latex. Later reinforced plastics where used. These plastics are
commonly welded by induction techniques. Also cast lungs are used, although
the reliability still has to be proved.
The counter lung volume varies tremendous. There are models
with a 4 liter up to 17 liter volume. Bigger volumes are employed when the
CL is also used as the main BCD, or life safer. Also surface swimming caused
a increased volume.