Heat barrier??

Customer in an apartment today, built in 1999, and we’re replacing the hob and fridge.

The fridge is under what will (when replaced) the ceramic hob.
Under the solid hotplate hob he now has is a square of what looks like plasterboard as a heat barrier.

Question. What will the material be, definitely not asbestos as building was done 1999. He’s adamant he wants something there and as I haven’t come across this before wondered what it might be or what i can replace it with?

Tony