Somebody asks a question about hearing protection and the anecdotal evidence comes pouring out of every orifice!
First, If you effectively plug your ear canal, your mastoid bone conducts sound with about 40 dB reduction over your open ear canal.
You CANNOT cover your mastoid bone as your complete skull is connected to the mastoid bone. The mastoid bone is what's discussed as the ear resides there.
practically speaking, you cannot get a muff to effectively seal to your skull, hence the common 25 dB NRR or so.
When discussing NRR you must understand what it means. OSHA rules say a manufacturer must measure the best attenuation a protective device offers then subtract the statistical error that can be caused by mis-application or poor inserting. In the case of a cheap foamie, the best attenuation is about 38-40 dB and the possibility if mis inserting is major! That is why foamies are rated around 26-28 dB. The muffs on the other hand do not have as much variability in fitting, but have way less attenuation at best hence the 26 to 28 dB attenuation.
Many folks use muffs over foamies. Why? Foamies, correctly inserted, afford the best attenuation available! And muffs do not make it any better as the mastoid is the limiting factor.
Personally, I use Etymotic Research GSB-15 electronic blast protectors. They are rated at 26-28 dB, but inserted correctly with the correct fitting tip approach 38 dB. And, they have a compressor amplifier that allows you to hear soft sounds normally and with very high fidelity. As the sound level goes up, the gain goes down till at an ambient sound pressure level of around 90 dB SPL, the gain is unity, or what comes in goes to the ear canal. However, once the sound level gets to 117dB SPL, the amplifier cannot go higher. So, if you are firing a large rifle with an impulse noise of around 160 dB SPL, your ear only hears 117 dB SPL of that for an effective attenuation of about 40 dB.. RIGHT! about the same as the mastoid bone! Can't get any better than that.
What gives me the right to say all these things? First, a BSEE as well as the graduate course in Audiology and a hearing aid dispensers license. And working in Research and product development for the ear the last decade of my career.