Anyone looking for GT2 Kevlar belts Reprap World have changed the URL from that quoted a number of times on this forum. Kevlar belts can now be found here:
Then you need to tick the box marked Kevlar under ‘Reinforcement’ near the top of the list on the left hand side of the page (I cannot find a direct link to the Kevlar page).
For what it’s worth the following paragraph is on this page - my emphasis. I quote without comment.
Next to glass fiber reinforcement we also have steel and Kevlar reinforcement, both reduce the elasticity and make the belt suitable for longer lengths.Steel is a bit cheaper. but is not recommended for applications with small diameter turns, i.e. 20 teeth pulleys.