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@JimmyTryhard
said, the tips will change the level isolation, as long as you're asking about different sizes. My isolation hierarchy is as follows: silicon < foam-filled silicon < foam. And as far as sound, it does change that too, minutely to my ears, but I'm not as discerning of an audiophile (though I don't consider myself to be an audiophile anyway, more as just someone who happens to enjoys music, headphones, and IEMs all at the same time
). For me, silicons offer the best seal, and as such the best bass response. Foams don't work so well in my ears, so bass response usually isn't as good for me, but it trims the highs a bit for the IEMs that are on the fence in terms of piercing treble. I don't listen closely enough for changes in sound with different tips and don't tip roll much, so I can't give you any meaningful overall opinion on the sound properties of different tips, but I'll say that my first priority is comfort and convenience. This is why my hierarchy for tip usage is more like this: silicon = foam-filled silicon > foam. Foams just don't work out for me so I never use them. Besides, different IEMs work better with different tips, I just happen to use silicons all the time as I don't have any foam-filled silicons around and the foams don't work out on my comfort and convenience scale.