Flexible grout

Hi,
I have underfloor heating with concrete screed and have fitted floor tiles with a flexible adhesive but haven't grouted yet. It was recommended to me that I use a flexible grout but I was wondering what kind of finish this would leave. Has anyone use flexible grout ? Is it hard-wearing ? Any other advice on grouting on UFH would be welcome.
Cheers
ennisjim

Yeah we used flexible grouting and have been in the house 2 1/2 years and no prob with the grout to date. Overall very happy with the underfloor heating. any questions just ask

Thanks rasco for the reply. A couple of questions...
- can you remember which brand you used ?
- does it dry hard or is it soft ?

Dries as hard as the grout used in the bathroom upstairs and that is not a flexible grout...now that i say that it kinda makes me wonder

Anyhow i cant remember the brand sorry about that and I only disposed of the excess recently