WHAT ARE THE BEST MATERIALS FOR CLOTH MASK FILTERS?
A Microscopic Study
By: Lindsey Krstic, B.A., R.N.
On the heels of my previous post are the results of the various filter materials that I looked at under my humble microscope. I have heard of a LOT of unusual things being used for filters (ahem- panty liners??) so I wanted to locate a few of those things around my house and check them out myself. I am also lucky enough to have an N95 respirator, a standard hospital-grade face mask AND surgical drape fabric that I can use to make a comparison from.
According to my research, both surgical masks and N95's are composed of 2-3 layers of 100% polypropylene, with the N95's having an additional cellulose-type layer- presumably, to be able to collect extremely tiny particles such as viruses. So, when you are viewing these fabrics as a single layer, keep in mind that the field isn't technically level. I would need at least 3 layers of filter material to be able to adequately compare them under the microscope which isn't really possible as by the time 3 layers are added there is not much to photograph.
To start with, I will show that hospital-grade materials look like under the microscope, and then will follow with the various home-based filter materials.
HOSPITAL-GRADE MATERIALS
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Surgical drape fabric
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| Hospital mask |
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| N95 respirator |
Not so bad, right? The N95 and standard hospital mask appear to block out everything. The surgical drape fabric is difficult to tell, as this is only a single layer (and there are two). But overall, it seems alright- definitely better than fabric. Next is the fun part!
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| Dried baby wipe |
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| Scotts brand blue shop towel |
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| Embroidery stabilizer |
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| Toilet paper |
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| HEPA vacuum bag (this one appears to be 3 layers- 2 of a polypropylene-type material, and a third of a thick-tissue consistency in the middle) |
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| Lightweight fusible interfacing |
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| Paper towel |
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| PM 2.5 disposable charcoal filter |
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| Polypropylene |
DISCUSSION OF RESULTS:
Overall, if I had to pick a material to use as a filter I would choose embroidery stabilizer as it is relatively inexpensive, easy to find online and have shipped, and can be washed along with the garment. The shop towels would be my next choice as they are fairly easy to find, inexpensive, and can be thrown away after each use. The HEPA vacuum bags don't appear to show any black background, but I would feel extremely uncomortable using these, as rumor has it that some of them contain fiberglass- and I don't know about you but I would NOT want that in my lungs. The baby wipes and lightweight interfacing in my opinion were the worst option, but if I had nothing else I'd still use them. While the polypropylene appears to show quite a bit of black background, I really can't say with certainty that it doesn't act as a good filter, because I cannot truly equate seeing more background with being less effective (perhaps the fibers themselves are transparent and therefore more background is shown). However, I do feel pretty safe in saying that the ones that are almost completely opaque would be a better option as an additive than fabric alone. I'm surprised by the toilet paper- it actually seems to be pretty decent. Although you'll probably find it easier to obtain any of the other materials these days.
Next, I want to look closer and layer up some of the filter materials to see if adding an additional layer would make a difference:
FILTER MATERIALS (TWO-LAYER)
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| Embroidery stabilizer (medium weight) |
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| Toilet paper |
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| Halyard (I added a second because it typically comes in 2 layers) |
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| Scotts brand blue shop towel |
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| Paper Towel |
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| Polypropylene |
Again, I would go with the embroidery stabilizer as my first choice because I could sew it directly into the mask and wash it at the same time but I'm also quite surprised by the toilet paper and would almost say that it is my second choice because it is cheap and most of the population has access to it, but I think the blue shop towels are still my solid second. Again, it would be wrong to assume that seeing more of the background means that it is less effective so I can't say that any of the materials are bad. But overall, I think either of these filter materials would be an important addition to your cloth mask and you just need to find the one that speaks to you.
That's it! I will try and update with more test materials as they become available to me. Hope you've enjoyed this little experiment!
