FYI, I have have two sets of EX71s and one set of EX81s, all purchased from audiocubes. There are two sections to both models' cords. In the case of the EX71s, both earphone and extension cables are made of the same material. In the case of the EX81, the earphone cable is made from a more rubbery, far less durable cable, that, after 3 months, is showing premature wear to the point that I have had to patch the insulation at two locations with electrical tape.
Soundwise, I recommend the EX81s as a low cost, better sounding alternative to the EX71s. Lack of durability eliminates this product though - I won't be purchasing this product again.
I would be curious if anyone is having a similar issue with the EX81s