well..here is more info:
Is it possible to install a cork floor over a radiant heating system?
Cork is a natural insulator and will affect slightly the transmission of heat. However, many installations of this type have been performed and without encountering any particular problem. Your floor may take longer to warm up but the heat will be retained more efficiently.
Only Natural Cork Floating Floor should be installed over radiant heating systems. Floating floors move as a unit since they are not attached to the sub-floor. That means visible signs of expansion/contraction take place at the perimeter only. Furthermore, adhesive used for installation of the tile could lose strength when exposed to high temperatures.
Certain precautions should be taken to minimize the effects of contraction and expansion:
Prior to installation over radiant heat, the slab needs to be heated and the temperature maintained at 75 degrees during installation.
As with any cork or wood floor installation, material must be acclimated in the room for 72 hours prior to installation.