They do both. Masks that effectively filter in both directions are much better at reducing transmission. Everyone should be wearing N95s or better whenever th

They do both. Masks that effectively filter in both directions are much better at reducing transmission. Everyone should be wearing N95s or better whenever they’re indoors with someone not in their household. As an aside, if you have a valved N95, just put some duct tape over the valve and voila, unvalved N95.