They block out too much noise in a lot of cases (especially those bullet-shaped orange jobbies with the 33dB attenuation). Without competing environmental noise

They block out too much noise in a lot of cases (especially those bullet-shaped orange jobbies with the 33dB attenuation). Without competing environmental noise, your own body noise (and there is a seriously big whack of that) becomes an enormous distraction. I loved them when I worked a hangar line around jet engines, but when trying them to get a bit of quiet in the office, I found that my heartbeat, my joints, the impact of my fingers on the keyboard and the sloshing of blood through the carotid arteries (which are way too close to the ears) constituted a distraction about on par with someone operating a jackhammer outside the window. Now, if there actually had been a jackhammer, the attenuation would have been about right. I found that the much less efficient silicon plugs were better for blocking low-level noise -- they didn't force the AGC circuits to max gain.