Bowers & Wilkins says:
C5 noise-isolating in-ear headphones bring you amazingly natural acoustics and fit so comfortably and securely you’ll hardly be aware you’re wearing them.
Available August 2011.
Tungsten Sound Tube
When it comes to in-ear headphones, nothing messes with your listening enjoyment more than a loose, unreliable fit. The C5′s inner casing is weighted with Tungsten, ensuring they are balanced towards the ear, not away from it. So the in-ear headphones will stay securely inside your ears throughout even the bumpiest bus ride.