Disco wheel arch paint stuff

On replacing my rear wheel arches I noticed that my 300tdi disco has a thick coating on the wheel arch. I had to grind a bit out to patch some places and it is almost like a spray on putty for lack of better description, it is flexible and look like it has probably been sprayed on then overcoated with a black underseal. It will also be helping with noise reduction so I am keen to replace this coating.

So if anyone knows what this stuff is called and where I can get it I would be keen to know.