cotton is absorbent u til it is saturated by moisture from your breath. about 20 minutes. Not that any breathable material protects from the virus anyway
I have never worn a surgical or cloth mask that became saturated, no matter how long I wore it. In any case, even if they become damp, water has a wonderful property of sticking to itself. Therefore, even a damp mask would attract any droplets containing virus. And if a mask became so wet that breathing became even more difficult than it normally is while wearing a mask, I suspect that most people would change it out.
Oh, and here are three papers that specifically address the question of mask efficacy in reducing the spread of Covid-19:
SARS-CoV-2 Infections and Serologic Responses from a Sample of U.S. Navy Service Members — USS Theodore Roosevelt, April 2020 [From the CDC's weekly publication, Morbidity and Mortality Weekly Report. And I know one of the authors.]
Face Masks Considerably Reduce COVID-19 Cases in Germany: A Synthetic Control Method Approach [Written by three economists and a statistician; however, their reference list looks solid.]
Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis [Published in The Lancet; most of the MD and MPH/MS authors are affiliated with Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, ON, Canada.]
All of these reviews concluded that masks (and social distancing and eye protection) are effective to reduce the spread of Coronavirus.
In addition, on the survivability of virus in different environments, I found this review: Stability and infectivity of coronaviruses in inanimate environments. Now, most of the studies examined in this review only looked for the presence of viral RNA in the environment, which tells nothing about whether there are infective particles in the environment. However, what that paper had to say about the survivability of virus on absorbent vs. non-absorbent surfaces was very interesting:
Infectivity of HuCoV- 229E was undetectable after drying on aluminum, sterile latex surgical gloves, and sterile cotton gauze sponges at RT for 3 h; HuCoV OC43 survived 1 h or less[34]. Contaminated droplets will be absorbed faster on cotton materials than on fluid-repellent materials, and cotton gowns offer protection against droplets bearing viruses. Droplets or fomites that persist on a nonabsorbent disposable gown or gloves may be a risk to contaminate the environment.
SARS-CoV strain GVU6109 was isolated from a lung tissue specimen of a SARS patient during the SARS outbreak in 2003[35]; its infectivity at 10^4 tissue culture infection doses (TCID50)/mL vanished within 5 min after drying on paper or a cotton gown at RT[35], showing that the viral infectivity perished faster on the cotton gown than on an impervious surface (e.g., the disposable gown) (5 min vs 60 min at 10^4 TCID50/mL, 1 h vs 24 h at 10^5 TCID50/mL )[35].
So it actually looks like cotton is the best choice for reducing virus spread.
But, don't tell me, I already know: what can a bunch of researchers who actually examine data and evidence possibly know about the real world?