The inner foam that we use is the exact same ester resin foam that is used in many high end commercial head sets designed for humans. Based on the materials used, the estimated decibel reduction is between 25 and 28, assuming proper fit and a good seal against your pup's head. That's 25-28 dB reduction in the human hearing range of 20,000 cycles per second, which is the only range that we have data for. Our canine friends can hear much higher frequencies (in the range of 43,000 cycles per second). As the frequency goes up, so does the effectiveness of Mutt Muffs, simply because the higher the frequency is, the more easily it is absorbed. Therefore, Mutt Muffs are especially effective at protecting against the high frequency wind whistles and shrieks we humans cannot even hear.
There is another factor that comes into play as well. The dog's own ear flaps are down and covering the ear canal, providing yet another layer of protection, better even than placing your hands over your own ears.