I couldn't find cases for the style of FFP2 mask that is currently quite common at least in my country so I ended up designing my own.

The model consists of two parts, the bottom and the lid and they are held together with magnets (4x2 mm in the current model, they are strong enough for this purpose). As the masks are somewhat ticker in the middle the lid goes on the inside of the bottom part and then pushes the edges down a bit. The current size fits three masks comfortably and four not-quite-so comfortably. I can also make a deeper bottom part if there is need for one that fits more masks.

The design was also affected by the print plate size of my Prusa Mini, Prusaslicer says the size as 179.99 x 179.99 mm when placed diagonically on the bed, making pretty much the largest size I could make it. The bottom edge is therefore 0.6mm thick (or thin) as a thicker one couldn't fit on the build plate and still fit the mask inside.

The included gcode files don't have skirts included for the reason above and I made the bottom layers with different patterns to make it easier to distinguish which one is the lid and which part is the bottom part.