- Certified fiberglass-free HEPA filter (or fiberglass-free MERV-16 if HEPA is not available)
- Spunbond polypropylene or clean non-woven reusable grocery bags made from spunbond polypropylene (not coated reusable grocery bags)
- Thin spunbond from hair nets or shoe covers
- Citric acid (or lemon juice)
- Low temp hot glue and gun (high temp hot glue tends to melt HEPA filters and spunbond too much)
Spray citric acid-water solution (¾ tablespoon of citric acid to 1L water) onto fabric. As long as you do not feel irritation while wearing it, you can spray as much as you can to improve performance against viruses. After spraying, dry it in a ventilated room.
If needed, remove the HEPA filter and flatten it. Cut the filter into the desired insert shape. HEPA filters often contain fiberglass and appropriate precautions are needed such as wearing a mask and protective clothing. Seal any holes in the HEPA filter.
Cut two layers of spunbond into the desired shape ⅜” larger than the HEPA filter.
Cut 1 layer of the thin spunbond polypropylene that was sprayed with citric acid the same size as the HEPA filter.
Assemble the 4 layers aligning the edges. The spunbond layer has ⅜” strip that will be sealed to ensure the HEPA filter is sealed.
Glue the all along the outside edges ensuring a tight seal is made. Press the edges together to ensure the layers are glued well.
Once the filter has been glued and is dry you can insert this into the pocket of your mask. These instructions are based on a template for a mask you can make yourself, but they can be modified to fit your specific mask by adjusting the template you use.