I think Peter is reffering to the thick (1″) lagging that they used on fusalage internal piping, forgive if I’m mistaken though!
This was made up as a very thick paste (usually the worst form of asbestos) and then spread over the pipe, it dried to form a thick layer of insulation. I have never seen a modern equivelent to this, however preformed foil backed fibreglass, or other more modern materials, including mineral based and armaflex pipe lagging, heavily painted over in PVC (ET-10) paint should give a very similar look.

I’ve never seen aircraft engine exhausts insulated though.