Filtration Basics

How can cloth stop a tiny virus?

1. Filtration of air doesn’t work as a simple sieve, only holding back particles larger than the pores. Some particles are stopped by running into the cloth, like a ball into a wall, this is called impaction. Others fall out of the air, called sedimentation. The random movement of particles causes further particles to be trapped, called diffusion.

2. The virus is small indeed, about 0.1 mcm, or one-thousandth the width of a human hair. However, most viruses in the air don’t exist alone but in respiratory particles, usually bigger and often much bigger than this, up to 100 mcm.

3. Woven cloth appears to have a regular structure with sometimes visible pores, but tiny invisible fibrils cross the pores and act as a barrier.

Our article in The Conversation on this topic is here.