What is your intended use for the sound-proof earplugs?
If your goal is to block noise while you sleep, you need earplugs that
are powerful enough to muffle ambient noises, from traffic to your
partner's snoring, and comfortable enough to wear for eight hours at a
time. For swimming, your main priority is whether the earplugs do a good
job keeping out water. If you want earplugs to wear to concerts or band
practice, you need a set that can soften sound without distorting it --
like turning down the volume knob on your ears. For riding a motorcycle,
look for earplugs that fit comfortably and securely under a helmet and
block out loud wind noise, while letting through enough traffic noise to
keep you safe.