Made of a sheet of glass with a frosted top. I've owned one for the last six months and it's been excellent. Very easy to clean with a wet wipe (I hate how grubby cloth mouse mats get), it hasn't worn at all and my mouse glides very smoothly and accurately.
I originally paid about £25 which is about the going rate if you hunt around. Play.com usually only have a few of their discount items in stock so this might expire quite quickly, but I hope not!