Flying beads
It's all a fur-fy (pun intended), with over 2000 hrs logged with the actual oxygen mask covering my mouth I can vouch for the fact that it does not leak with a full beard, I wore a beard for 33 years until some so called chief pilot or whatever at Ansett threatened us with our jobs if we didn't cut them off. Started re-growing it the day I retired. When I first started in the job in the back of a DC3 I did a de-comp check with the RAAF and the operator there told my boss that the beard makes a labyrinth seal with the face and can in most cases be a better seal than skin. The test was to FL350 and about 80% of ops were above FL250. As you suck to breath the mask squashes against the face, it is supposed to be tight as well anyway. The note on the side of most masks I used only stated that it hadn't been tested for use with a beard, not that it didn't work with a beard, it worked for me and thousands of others