The Custom 3 headphones have special oval ear tips made of soft, lightweight silicon that come in five sizes (an assortment is included), which allows them to create a near-perfect acoustic seal in your ears. Coupled with an advanced driver and crossover system, the Custom 3s deliver excellent bass response, pristine highs, and amazing stereo imaging. I've been using these phones regularly when riding to work in a noisy commuter train, and they are the best I've heard. My only gripe is that the thin, fabric-covered wires tend to tangle easily. As with most high-grade in-ear monitors, the Custom 3's aren't cheap, but if you're looking for the best possible sound from your iPod or other portable music device, these phones definitely do the trick. —Art Thompson