The Invisibobble is described as a 'traceless hair ring' which means that it will not leave a imprint or kink in your hair at all and boy does it work wonders. Funnily enough they remind me a little of old telephone cords.
When I remove the Invisibobble after a long day I put it away and it pings back to it's original shape and size as it's quite stretchy and flexible, it's pretty much like a spring. I don't see myself using another hair tie anytime soon, they're amazing.
You can purchase the Invisibobbles online here from Feel Unique for £4.95, not bad eh?