For clarity, photos of the Sensaphonics custom Shure sleeves (shown with SE425). The added isolation is due to deep insertion, past the 2nd bend of the ear canal. The soft silicone also flexes with your ear canal, maintaining the seal. BTW, Sensaphonics offers bundle deals for the SE846, SE535, and SE425 combined with custom sleeves that can save you a few bucks. They also make custom sleeves for most (not all) other Shure IEM models.
3/7/14 at 2:33pm