Earmuffs have hard plastic cups with soft cushions that seal around the ears to block noise. Usually, an earmuff with a higher NRR rating tends to be larger (bigger cups with more sound absorbing foam) than an ear muff with a lower NRR. Though none will completely eliminate noise, they will reduce the volume, especially at the high pitched end of the scale. The two basic designs of earmuffs PK Safety stocks are over-the-head and cap-mounted. The cap-mounted earmuffs are designed to fit directly on most hard hats that have side accessory slots.