See the "Documentation" section - it's easy to see how the mask works through pictures.

 

Inspired by interchangeable lens systems on DSLR cameras, this mask is designed to make it easier to experiment with different materials (some seem good until you try to breath through them while doing things, and it takes a lot of work to sew a mask), because I noticed that I was really only breathing through a small part of the material in front of my mouth/nose (so creating separation allows air to pass through a greater surface area), and because the amount/type of filtration I might want to use changes in different situations (as activities and risks are balanced). 

 

The mask holds "filters" of several sizes such as Aeropress coffee filters (I've read that these would need to be replaced with every use), whatever other materials you can cut circles into like fabric/sheets, and readily available 70mm filter paper. There's plenty of room to layer and space them, and I've read that there are benefits to mixing materials. Because of the added space, it is much more breathable than wrapping the same materials directly around the face and you have some flexibility to mix & match parts to make it more breathable or less large. It also uses much less material, so sheets of one-time use materials can be cut into more masks for more outings. Since it's modular, you can replace the filter-holding parts with your own designs to accommodate your own solutions, and you can do things like add/subtract filtration layers on the fly without having to take the mask off (perhaps as you balance risks with breathability and physical activity), swap components for fresh ones or for different situations as needed (like when material gets wet), and adjust the mask without having to touch the filtering materials (so you can avoid contaminating your hands with whatever the mask caught).

 

This mask hasn't been experimentally tested for efficacy and you'll have to use it at your own risk, but it might be a good option for people that have no other choice but to make their own mask. Also, be sure to read up about good mask-making materials because more information is coming out all the time.