This wind instrument double-layer cover is designed for bell sizes ranging from 12″ to 13″. This bell mask is perfect for the tuba and other large bell instruments. It covers bell openings to greatly reduce the spread of aerosols. This bell mask is made to meet performing arts aerosol study recommendations, and is equipped with a removable MERV 13 filter. The breathable design adds little to no back pressure or acoustic loss during a performance. The elastic closure and cord lock keeps the bell mask secured to the bell opening. Made of non-woven polypropylene fabric, it’s reusable and hand washable. Be sure to measure instrument bell to guarantee the best fit.Disclaimer: These masks have not been tested by the FDA, CDC or any other official organization to conclude that they prevent the transmission of viruses.