Tested Technology explains Hi-Res audio with some help from the Optoma NuForce HEM4 in-ear headphones:

“The technology is genuinely serious too—this is definitely not a Beats-type stitch-up.”

“…the HEM series uses a curiously snail-shaped enclosure made of Lexan, a proprietary lightweight thermoplastic polymer resin used in jet fighter canopies for its strength, impact resistance and—particularly significant in audio applications—mechanical stiffness.”

“The stiffness of Lexan resists the tendency of the HEM4 enclosure to resonate in sympathy with the sound waves being delivered, so you get nothing more nor less than what the input signal is meant to deliver.”