From D'Addario:

D'Addario Pacato hearing protection is a reusable, universal sized audio filter designed specifically for musicians and music enthusiasts. While traditional earplugs can sound muffled and unnatural, the Pacato filters provide full frequency, enjoyable audio at safe listening levels. The exclusive design offers an open air passage to the ear, minimizing occlusion effect (low frequency emphasis), while keeping the ear ventilated for unmatched comfort.