The 'cool' is literal. These are double-walled glass cups, with a vacuum seal -- nice to your hands while your tea remains piping hot. Made by teasetc. and sold in twos.
I just got them from Amazon and am thrilled! Tea just looks beautiful in them, the color and clarity enticing. They are surprisingly light but sturdy, microwave and dishwasher safe. And the size is just right at eight ounces. Bodum's Pavina cups are similar but a bit larger at 8.5 ounces. Some Amazon customers had found the thin walls a bit too fragile so I didn't go for them.
I have come to like the lack of a handle. It invites you to 'cup' the cup with both hands -- and somehow that seems more 'natural' for tea. 
The ideal use for these cups would be to put in them the stunning origami crane teabags designed by Russian designer Natalia Ponomareva. Unfortunately, as far as I can tell these exist as a packaging concept only.