Howard Leight Thunder T3H Black Helmet Mount Noise Blocking Earmuffs with 27 dB NRR have dielectric construction and enhances worker safety by blocking noise in electrical environments. Plastic earmuffs feature a patented Air Flow Control? technology for optimal attenuation across all frequencies. Earmuffs have snap-in ear cushions that make replacement fast and convenient and feature a quick click height adjustment. For use with a wide range of hard hats, and earcups snap in place during use and swing back when not in use.