The IS-MIX is a field-use, mechanical re-breathing apparatus. It has a constant oxygen concentration regardless of the diver's workload and diving depth. The semi-closed system allows a very low oxygen consumption independent of diving depths and ensures longer exposure times through a low nitrogen partial pressure in the Nitrox gas relative to the air.

The IS-MIX has a low breathing resistance due to the weight of the bellows compensating for the hydrostatic pressure difference. It has automatic volume compensation through a hydrostatic valve that adds more gas to the breathing circuit when the bellows are compressed during rapid descents. In addition, there is a dosage warning which monitors the gas dosage and the tightness of the breathing circuit. The diver can also manually supply gas using a by-pass arm in cases of failure. A reserve gas valve prevents the diver from unknowingly using up the entire gas supply.

The IS-MIX has a gas supply with a gas cylinder of 5 dm3 of 300 bar, which gives 1,500 dm3 gas (1,350 dm3 amount of free gas having a compressibility of 1.1, i.e. the compression of gas is not linear at a pressure above 250 bar.). Where longer action times are needed, the IS-MIX external gas supply, DPX, can be used.

The reserve gas valve is triggered when the pressure in the gas cylinder is about 20 bar.