Low-cost measurement of facemask efficacy for filtering expelled droplets

I think the broader point is one that still stands: wearing literally anything over your nose and mouth is shown, by this study, to cut droplet by at least 50%. Even the cotton varieties cut it from 70% to 90%. So...people need to just slap something over their two air exchanging orifices on their faces before leaving the house and contribute to the our greater health.

You're right about the differences in effectiveness but 70% is still pretty good as long as many people are wearing something and not exposing their noses or wrapping the mask lovingly around their chins.

After looking at the article for a while, my take away was material aside, the fit matters a lot. They got a very different results with the same materials with different fits. I know from using one the peaked N95 has an awesome fit. I guessing the swath was pressed hard to the face, so no leaks which would explain it's good performance. The best of the cotton masks was again the peaked.

Fit being important isn't good news. You can get a good idea of the material from the ad, but judging fit is hard without trying it on.

The values on N95 can work both ways - allowing air to more easily pass in the in or out direction. If it's in I guess it's not protecting you so well. If it's out it's not protecting others. Out is what they tested. Most seem to be out, but I have one that's in (maybe a manufacturing fault - who knows). It's nicer to wear for long periods than out. In the context of slowing down covid, I'm guessing in is more effective.

A couple of reasons for this spring to mind immediately. Firstly, governments don't want people using the most effective masks because there's barely enough of them to supply hospitals. Secondly, the push for masking has absolutely nothing to do with effectiveness. For instance, people keep pointing to things like the 1918 flu epidemic as proof we've always known masks worked, but as far as I can tell those masks were made of gauze and therefore likely as bad as or worse than the worst mask in the study. And there was an article going around pointing to this study of the effect of reducing the dose of flu virus people were exposed to as proof masks worked better than expected: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4342672/ Notice how, at the part of the curve where reducing the amount of virus had the most effect, it took a tenfold reduction or so to reduce the number of people showing symptoms or testing positive by about 30%? On its face that seems kind of bad for the idea of using random non-medical face coverings with much worse filteration, but that's not how it's been spun.

Also, I think a lot of this has to do with what people feel will work based on it having a good narrative attached. For example, there's this fairly widespread idea that valved masks are not OK and worse than random cotton face coverings which I think has even been enshrined as an actual legal requirement in a few places despite clearly not matching up with the test results here. Presumably this is because it feels like deliberately letting your own breath out past the filter via valves is intentionally exposing others, even though anyone who wears an ordinary non-fitted face mask can easily notice that exhalation blows out around the edge of the mask anyway - often with really annoying results for glasses wearers. A bunch of British news organisations even accused our government of telling people to wear "useless" maasks and endangering the public for showing a valved mask in their advice: https://www.independent.co.uk/news/uk/politics/coronavirus-f...

The authors themselves point out the valved N95 masks might be worse than what the raw results show:

"Furthermore, the performance of the valved N95 mask is likely affected by the exhalation valve, which opens for strong outwards airflow. While the valve does not compromise the protection of the wearer, it can decrease protection of persons surrounding the wearer." [emph. mine]

Table 1 gives the relation between mask names and numbers.

Having to use the table to relate the pictures to the results does seem very poor.

I don't think there's any reason to assume vapour from a pen resembles the droplets in your breath. In fact, that one of them is visible and the other is not should suggest that they might behave very differently.

From first study: "The null hypothesis is that there is no difference between medical masks and cloth masks. ... The control arm was ‘standard practice’, which comprised mask use in a high proportion of participants [NOT "mask free"]." -- this means "increase relative to surgical masks", not relative to no mask.

Second study is only N95s. Just don't wear an N95 if you need more air for aerobic capacity. The OP study shows that they're not _that_ much better than surgical masks anyway.

But hey believe what you want to believe.

This is a bad faith post intentionally spreading misinformation.

Ignoring the quality of these studies, the first concluded that cloth masks were less effective than medical masks, not that the are worse than no mask. It also evaluated and discussed the use of cloth masks to protect health care workers, not to slow the spread of sars-cov-2 via respiratory droplets.

The second, tiny, study says nothing about damage. Their results suggested that surgical masks reduce cardiopulmonary function slightly with surgical masks and a little more with N95 masks.

The question is whether I trust your "survey" or the CDC's recommendation.

But also, in both cases based on a quick skim it seems to me like you're misrepresenting the studies. In the first study, the control was "normal practice" which included mask use. In the second study, I see no claims about cardiac damage; I understand it to say that masks make it harder to breathe, which is useful information but not very surprising.

The title of the first study is:

A cluster randomised trial of cloth masks compared with medical masks in healthcare workers

Not only is your presentation of its results in bad faith, you rely on people not reading the article.

We’ve also had studies which claim something along the line of ”Apples cause cancer” and the truth is that it happens only under some certain rare conditions and even then one might have 0.01% chance of increasing their chance to get a cancer by 0.1%. But hey, that’s an increase in possibility nevertheless!