Haven't touched it yet, so will try icy cold water, thanks. We have a mattress cover, but as we took it off recently for a wash and didnt' put it back on as realised it might be making us even more hot! I think this would have soaked right through anyway. But at least we can cover it up, because i can't imagine I'll get it all out. Also, can turn the mattress, I guess!
Thanks everyone