The good breathability of polypropylene bags means they can be layered up to make more effective DIY masks, although they still do not come close to the performance of a surgical mask.
We measure the ability of the polypropylene bag and other materials to capture 0.3 micron particles and 1 micron particles. The COVID-19 coronavirus measures 0.06-0.14 microns by itself and 5-10 microns when in water droplets.
1 layer: able to capture 22% of 0.3 micron particles, and 42% of 1.0 micron particles;
2 layers: able to filter 34% of virus-sized particles;
3 layers: able to filter 57% of virus-sized particles.
Click here for more data and details: https://smartairfilters.com/en/blog/nonwoven-pp-shopping-bag-diy-face-masks-covid-19/