As stated above, the NRR of the foam plugs is higher than the custom molded plugs.
I have 2 sets of custom molded plugs - one set made from relatively hard plastic (EAR) and the other from a softer/pliable silicone. The silicone plugs are very comfortable as Stan stated. When on the clays course, I typically wear a foam plug in my left ear (RH shooter) and a molded silicone in the other. The advantage of doing so is that I can easily crack open the silicone plug's seal in order to hear a conversation and then push it right back into place.
In an effort to better deal with the impulse noise from a shotgun blast, I selected the lead shot-filled silicone models from Northwest Hearing Center. Had my impressions made locally and then sent them to Northwest (very fine folks to deal with).
