While it cannot be used directly on top of it, it can be used in conjunction, Kingspan have a great guide for this depending on your set up - https://www.kingspan.com/gb/en-gb/products/insulation-boards/insulation-technical-hub/articles-and-advice/underfloor-heating-and-floor-insulation#:~:text=Floor%20Constructions&text=Insulation%2C%20such%20as%20Kingspan%20Kooltherm,thermal%20mass%20of%20the%20floor.