Sadly, I can't remember where I first came across this idea so I can't give proper credit, but needless to say that the original idea was not mine.
What I do remember, though, was seeing a photo in an up-market magazine (possibly Scottish Field) and thinking '£70 for a cashmere-covered bangle - what a rip-off'. So I, in turn, ripped off the idea and made this alpaca-covered bangle for about £3.50.
The core bangle is a cheap plastic one from Claire's Accessories. I then cast on 64 stitches with Artesano Alpaca Inca Cloud yarn on 2.25mm DPNs and away I went. I had thought about grafting the end to the beginning, but to get enough tension to keep the cover taught, I ended up casting off all the stitches, then using a varient on mattress stitch to bring the ends together.
I really like this (and it keeps my wrist lovely and warm) and am now on the look-out for other old bangles of various width to cover.