This deep dive post looks into the “Big Four” criteria evaluated in preliminary assessments of community mask materials: material characteristics, breathability, water-repellence, and disinfection options. More specifically, we focus on nonwoven polypropylene (NWPP), which is commonly used in commercial face masks. Although ideal medical grade NWPP is not currently available for community use, NWPP is commonly available at different weights and grades for other household and/or commercial purposes, such as reusable grocery bags. Here we take a more in-depth look at the 4 preliminary criteria considered when evaluating potential sources of NWPP.
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.