Bought these filters for four years now. My wife is a teacher and requested some type of filtration system for her classroom Merv 13 filters are said to be good enough to filter Covid viruses and other small viruses. I built her a four filter box fan filtration system. Covid scare is over, but my wife noticed how many less colds her students had and has requested me to make a new one for her every year since, good quality filter had a reasonable price