It depends on the product.
Universal Trim-to-Fit Filter—One size fits all.
ComfortSeal Filter—Currently available in 3 sizes. “Medium” normally fits average-sized faces—faces in which the distance between the upper part of the chin bone and and the bridge of the nose is 2.75″ to 3.125″. “Small” normally fits smaller adult or adolescent faces—faces in which the distance between the upper part of the chin bone and and the bridge of the nose is 2.25″ to 2.75″. “Large” normally fits adults with larger or longer faces—faces in which the distance between the upper part of the chin bone and and the bridge of the nose is 3.125″ to 3.5″.
