What's Really Best Filter?

As a non profit founder of Fashion Girls for Humanity, which has provided free patterns for PPE masks and gowns (now 100,000 people accessed from over 155 countries), I learned a few things about materials and filters. None of the data here is verified independently by us, but we want to share these articles and want to share. For convenience, we offer a generic filter for purchase together with our masks from here. I personally like the idea of using an old scrap fabric (silk or chiffon) as an insert as suggested by Boston Globe. 

• The CDC suggests using a coffee filter, which is readily available in many homes. You may also consider using part of a HEPA vacuum bag or air conditioning filter (look for products without fiberglass).
• Boston Globe reported that researchers say some fabrics can filter nearly as well as an N95.  A combination of cotton with silk, chiffon, or flannel can create a well-functioning filter.  The best overall filtration was provided by a sandwich consisting of one layer of the tighter-woven cotton plus two layers of silk, or two layers of chiffon, or one layer of flannel — because of the electrostatic filter created by the non-cotton layers. So imagine our masks made of silk or cotton to create an electrostatic filter by inserting a different material. According to the research, the hybrid improves the efficacy and may enhance the performance. But there’s a big caveat: If your mask leaks around the edges, unlike the tightly fitted N95, your homemade filter will lose its effectiveness.
• Filter information and testing from Threadsmonthly.com (April 2020)
• The filter effectiveness information from smartairfilters.com is useful (Updated May 2020)