The MakerMask project team has reviewed extensive literature on the science and manufacturing of NIOSH-approved respirators. We selected a multi-layered design that balanced increased filtration capabilities with permeability for breathing. The spunbond non-woven polypropylene (NWPP) outer layers use the same type of material used in medical-grade commercial masks, providing water-resistance for blocking droplet transmission and mechanical filtration from the structure of the fibers.