This perhaps?
Follow the link and scroll down. You’ll find a couple of links to study reports. One of those links is the one that you’re looking for.
Can DIY Masks Protect Us from Coronavirus? (with links to research reports)
https://smartairfilters.com/en/blog/diy-homemade-mask-protect-virus-coronavirus/
What Are The Best Materials for Making DIY Masks?
https://smartairfilters.com/en/blog/best-materials-make-diy-face-mask-virus/
Dish towels seemed to work the best for a DIY mask. Paper towels not so much.
Oh, if you really want a really effective paper filter, vacuum cleaner bags are really good, but really hard to breathe through.
i read that the SARS virus was 1 nanoparticle (or was it .1 - can’t remember now-) but also read that typical masks don’t stop particles that small- none of them do- except for the really secure chemical filter ttype masks that are near impossible to breath in-
I suppose masks might filter out a small % of viruses that small, but I think most of the particles are getting through- but i suppose even a reduction of chance to 1/3 would at least be something- but if sneezing and coughing and just talking spew out clouds of virus, and most make it’s way through a mask, what god is wearing the mask really? there will still be a cloud left behind that folks will walk through- even if it is a reduced cloud- it seems that wearing the masks only slightly reduces the chances- Better than nothing? I guess- but still, in a room full of people, many particles are making their way out into the air if masks don’t stop particles that are 1 nanoparticle small or smaller- nooen knows how small the corona virus is yet- -
The two or three layer fabric masks with a filter pocket, with a folded paper towel inserted in the filter pocket will be about 80% effective. This is about as effective as we can get with homemade protection.
I would not rely on a mask made exclusively from paper towels. It won’t last and it won’t seal.
The masks I made for my two daughters who are a nurse, and a director of food service for major hospitals in heavily populated areas:
https://www.youtube.com/watch?v=zm_NmpdgWWA
I heard if ya cut your wife’s bra in two and use one of them as a mask, they’re effective in stopping 82 percent of cooties. Plus you get two masks for every bra ya cut in half.