Using this wind instrument cover is easy. First, measure your instrument bell to make sure it's between 22 and 23 inches. Then, place the cover over the bell opening and use the elastic closure and cord lock to secure it. During performance, enjoy the breathable design with no worries about back pressure or acoustic loss. When it comes to the MERV - 13 filter, don't wash it. For best results, replace it every 1 - 2 months. The cover is reusable, so when it gets dirty, just give it a hand wash. Keep in mind that this cover hasn't been tested by official organizations for preventing virus transmission.