Hi, this is a work in progress right now.
The mask will have a 0.4mm thickness (height) but maybe less.
This shape is not the final one as this is only my first prototype and I'm doing it really quick by iterations. The first design was a fail and I started over with this one.
At the bottom you can see a Bezier Curve that defines the shape. I duplicate it and make a mirror on X, then join the two parts. Transform to Mesh, then Extrude to give it 0.4mm height.
On the top you see the "air entrance hole" shape which is also a Bezier Curve. To make the grid I use the Tissue plugin with a small square component applied on a Plane (hidden in this screenshot). I use a boolean operation to find the intersection of the Air hole shape and this grid so it takes a Oval shape.
I do another Boolean operation to assemble the main mask and the grid.
The V shaped parts are made to give the good final shape to the mask and needs to be tested, but normally it should work. The shape of the "hooks" may change and again, this is only a prototype.
The exported STL was so dirty that it's not yet printable and I'll have to do it with a better method : all 2D until a last and unique Extrusion should produce a nice STL.