Vented Sleeve for the Sony CRE-C20 Self-Fitting OTC Hearing Aid Each package contains 3 pairs of vented sleeves. Sleeves available in four sizes to account for different size ear canals: XS, S, M, and L Can be adapted to fit most ears and hearing needs. These sleeves are not compatible with CRE-C10 and CRE-E10 These vented sleeves let more sounds through than closed sleeves included in the C20 kit, which helps prevent that uncomfortable feeling of plugged ears.