The powder-puff box has a clear lid, this is the window the user looks through.
The bathing cap is the mask that fits about the face.
There is no valve. The breath goes in and out through the filter.
The charcoal/soda-lime mixture is wrapped in two layers of hanky and packed into the can.
The pieces of screen are taped over the ends of the can and any excess cloth cut off.
Then the can shoved into a hole in the mask and sealed on with tape.