Cup style

Stiff enough to stand up on its own means it is going 

to hold a 3D cup away from your nostrils and lips:

Template

Sewing it

You would use black thread. I used red as it is 

easily to follow for others who'd want to make their own

More details

Three layers of 80gsm SBPP and one of 38 gsm for about 77% F.E at 28.3 liters per min

... not counting for edge leaks. ✓ Washable ✓ VERY breathable MakerMask.org data - LINK - gives us the 77% F.E. This could be made with more layers - four of the 80 gsm easily, but six would be a challenge.