I've always associated zirconia with cheap jewellery from TV shopping channels, but Panasonic have seemingly chosen it for its ability to quell sound-distortion rather than its faux-glamour. Their RP-HJE900 earphones feature zirconia casings that have particularly low resonance level, unlike traditional plastic shells. They're also much stronger than plastic, and resistant to scratches.
Zirconia is both a high-density and high-rigidity material, hence being compared to diamond (and made into often-tasteless shopping channel rings). Panasonic claim using the material produces sound more accurate to the original recording; having not tried them myself, I can't comment, but I'd suspect that encoding your digital music at a higher bit-rate might have more of an affect than what your earphones are made from. Sound pressure sensitivity is around 100dB/mW, frequency response is 6Hz–28 KHz and impedance 26Ω.
Seemingly for transport purposes, the RP-HJE900 set feature cables that can detach from the earbuds themselves. I suppose that could be useful if the cable tears or gets accidentally cut. They'll be available in Japan, at first, on June 15th; price is as-yet unannounced.