I'm assuming you mean the Sensaphonics silicone custom sleeves. The custom sleeves are custom molds of your own ears, inside the second bend of your ear canals and out, so yes, they...isolate better.
Better isolation means everything is more pronounced through the whole audio spectrum, lows, mids, and highs. I will use the word "felt" instead of "increase". You actually feel the music more, very difficult to quantify. But once I get my review posted, everything will be much more in depth.