Listen To Your Ears. Your hearing health should never be ignored. SureFire EP4 Sonic Defender Plus will protect your hearing against Noise-Induced Hearing Loss (NIHL) without compromising your ability to hear routine sounds or conversations in noisy environments. Their triple-flanged-stem provides a Noise Reduction Rating (NRR) of 24 dB. Safe sound levels are allowed to pass through into the ear canal, while potentially harmful noises (above 85 dB) are reduced via our proprietary noise-reducing filter. EP4s include attached filter caps that can be inserted for additional protection, blocking out lower-level noise, like that heard on an airplane, where hearing ambient sounds or conversations isn't critical. Sonic Defenders are made from a soft, durable, hypoallergenic polymer that provides all-day comfort and extends product life (up to 6 months, depending on usage and care).