I have tried both, acrylic and silicone. I've also had ones made by UE as well in the past. None of my acrylic customs have ever matched isolation of customs from Spiral Ear. For me, the overall isolation is also better than Etys with triple flanges.
I've found an excerpt from my previous emails with Spiral Ear:
'Regarding noise reduction, it’s not model dependent and all of our monitors will equally reduce ambient sound.
An average isolation of our monitors is ~ -37dB, however, it is really a case by case scenario depending on individual ear anatomy (and whether it’s possible to accommodate longer canals in relation to one’s ear anatomy).
It's our standard to make custom IEM's with musician's fit, i.e. the longest canals possible, but also striking a balance with optimal comfort levels whenever possible.
Medical silicone that we use provides the greatest isolation levels out of any custom IEM’s available on the market (again, highly dependent on one’s particular ear anatomy). Etymotic IEM's provide one of the best noise isolation in universal form with triple-flange tips. Our custom monitors will provide on average a similar level of noise reduction in overall spectrum, and in some areas (like for example furthest reaching long bass waves and mid frequency sounds) they should provide better isolation due to covering more concha and outer ear with silicone, not only the canal area.
Please note that it is physically not possible to fully isolate oneself from any ambient sound with any material and it is not possible to eliminate that by using solely IEM's (and it's true for any IEM's or custom IEM's), because human ear is fed sound waves through bone conduction and skull- directly via cochlea, apart from ear apparatus only. All these areas would have to be fully covered apart from using best sound-deadening custom IEM's in order to approach that level of sound isolation.'
