Just a general note- how well a hearing protection device works is indicated by a number- the NRR, or Noise Reduction Ratio- usually marked on the package. The higher the number, the better it works. However, because sound is on a log scale, 1+1 does NOT equal 2. If you have plugs that are 30, and muffs that are 22, wearing both does NOT get you 52.
Most muffs or plugs work by providing layers of soft material that aborbs sound. Some VERY high tech electronic muffs actually generate sound that is 180 degrees off from the original sound wave- and CANCEL the sound. Other electronic muffs are really just sound deadening muffs with a mike and speaker- which cuts out when sound goes above trigger level.