Turns out two layers of 100% cotton is 69% efficient at blocking particles the size of viruses - not as good as a mask which is 97% effective, but way better than nothing (especially if worn over a mask).
You really really really misunderstood that study. Two layers of 100% cloth is about 3% effective compared to a medical masks 56% effectiveness. And as for preventing infection it was actually worse than the control group.
There's some question if its better than nothing. The study even says one possible conclusion is that it is in fact worse than nothing.
The control arm was ‘standard practice’, which comprised mask use in a high proportion of participants. As such (without a no-mask control), the finding of a much higher rate of infection in the cloth mask arm could be interpreted as harm caused by cloth masks, efficacy of medical masks, or most likely a combination of both.