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Particles in between those sizes (around 0.3 microns) don't travel in straight lines and also don't zigzag randomly but get carried along with the air as it flows around fibres and likely past fibres so can possibly sneak by respirators even with multiple layers. N95s use a final trick of capturing particles of all sizes using an electric field where even neutral particles will still be attracted (as you can see from neutrally charged styrofoam sticking to a cat with static charged fur). 14/