Exhaust wrap?

[Gnasher]

I thought it was developed for car racing to keep the under bonnet temperature down

It's been used in many applications for well over a century.  It's really just lagging which was used on steam engines to keep heat in the transfer pipes and to protect people form touching hot pipe work while working.  It's been used on aircraft exhausts to protect fabric fuselages or to stop heat transfer in engine bays still used my mates plane engine has it.  Yes it's been used in cars and most likely before bikes, to my knowledge it started being used on bike exhaust systems in the early 50's when full firings began to appear on speed record and racing bikes.

My earlier statement was just referring to it's application on bikes.