From https://smartairfilters.com/en/blog/diy-homemade-mask-protec...
> Data shows that homemade masks made with a single layer of cotton clothing, or a tea towel can remove around 50-60% of virus-sized particles.
> Data shows that homemade masks made with a single layer of cotton clothing, or a tea towel can remove around 50-60% of virus-sized particles.
That's not to say do or don't do it, just be careful. Handwashing and not touching your face are the single most important things to do.