How should I breathe through the mask (through my nose or mouth)?

You can breath through either or both. In short which ever is most com­fort­able for you to main­tain a mod­er­ate breath rate. Both LiveO2 and ExtremeO2 work regard­less of how you choose to breathe.

If the mask is fit­ted prop­er­ly you should have no dif­fi­cul­ty breath­ing in through your nose. If this is dif­fi­cult, move the mask high­er on the bridge of you nose, inflate the cush­ion a lit­tle more and or loosen the neo­prene straps slight­ly.

Most indi­vid­u­als will breath through their mouth when breath­ing hard but this is not nec­es­sar­i­ly the most effi­cient way to breathe.

Yoga sug­gests the best breath­ing method is to inhale through the nose with the tongue on the roof of the mouth and then exhale through an opened mouth with the tongue flat and relaxed. However, this can be chal­leng­ing when exer­cis­ing vig­or­ous­ly. During exer­tion, breath­ing through the mouth is typ­i­cal, espe­cial­ly with high alti­tude, like with ExtremeO2. Just breath any way that feels good. The main objec­tive here is to bring the oxy­gen from the sys­tem into your body.