Anyone know if there is some self adhesive insulation that can used on the inside of the decorative plastic engine cover ?

Mine disintegrated years ago. Just took the remnants off and vaccuumed the top of the engine to get the foam bits off. Can't say I noticed any difference in noise etc.

I ran my mk2 with no engine cover for about 6months and my old 1.9 mk1 octy for 2 yrs and also didn’t notice any difference in engine noise while driving..

Apart from it being decorative, is there a reason why you want to keep it?