A local organization is looking to produce masks for the hospital, and they reached out to me for guidance. Since this is outside of my expertise and I haven't been following all of the recent research, I'm passing the questions along here.

We are looking for some valid research on the use of commercial products for face masks. We have a couple of designs that can fit over or have a pocket to insert an additional filter. I have found multiple sources online that refer to furnace filters, air filtration system filters, even HEPA vacuum bags, as ideal products to use to either completely comprise a face mask or be inserted into a pocket between layers of fabric to provide extra protection.

My questions are:

• Which of these products are or are not safe to be breathing through? The only caution I have found is to be careful to check for fiberglass in the content.

• Which are most effective, or does it come down to the MERV/MRP rating? We have been looking at filters at MERV 13-16 and/or MRP 2500-2800 in range. Are these safe as long as they can be breathed through?

• Can these types of materials be layered to provide extra protection i.e. is layering two ply of MERV 11 like a MERV 22 or is there a loss ratio? Is there a formula which can be applied?

• Could other materials be used to enhance the filter’s effectiveness, safety, smell, etc.? I have seen models that added an activated charcoal filter over the top, coffee filter, etc.? I have also heard that layers create a dispersion effect that increases the protective factor i.e. a thick bundled knitted scarf has a higher protective factor because of the density.

There is so much out there but it is mostly DIY crafters, and I am interested in a more empirical opinion!

Karen Kempton

Karen Kempton