*     with 2 Dome - A second dome above the air outlet prevents the exhaled air from escaping unfiltered.

**    Valve Lockable - A blocking cap or a 2nd dome prevents the exhaled air from escaping unfiltered.

***   Visor as accessory - Transparent visor / face shield can be integrated directly into the breathing mask as an accessory.

**** Temperature Dead space - the area in the mask where exhaled air remains, which is the first air to enter the lungs when inhaled. If this is too large, too much CO2 is inhaled.