Iride01 

Nothing magical. Just things people have known for many more years than I've been alive.

If you have more surface area in a filter of any sort, then more volume of air can flow through. More volume passing through at any one moment means easier breathing. Pleats give you the ability to have more surface area in the same space compared to no pleats.

I thought I'd already mentioned that sweat or any wetness will significantly reduce airflow whether pleated or not. So anyone wanting to wear a mask should take several.

Capricorn2

I do not think that this is necessary, especially since there is no obligatory mask regime outside.