I was going to be clever and call this thread "A hat for my head" or something like that, but decided not to.
I've seen much discussion here lately over hood and engine bay insulation. I figure, whatever heat I can keep inside the engine won't have to be trapped by a leakier hood insulation setup. Of course you can't wrap the whole engine but I certainly could wrap my valve cover.
Future plans call for an outer cover to be made from 1" or 3/4" foam insulation. Sort of a rectangular hat to slip on over this very close fitting setup shown below. But that's for another day.
This stuff is about $6 per roll at Home Depot. Armacell pipe insulation. It's intended to be wrapped around plumbing pipes. It works very well in a hot engine bay.
It has a peel off backing and a sticky underside.
It also has fibers running lengthwise and crosswise. This prevents the material from stretching so it keeps its proper thickness, 1/8".
To help it stick, I used brake cleaner to clean the dirtier parts of the valve cover. The worst area was behind the filler hole, on the vertical back face of the valve cover. The valve cover still looked pretty bad even after a scrubbing, but the insulation stuck very well. After driving a week, an hour each way to work and back, the insulation stayed put.
I laid down multiple layers. It's four to five layers thick, depending on where you check.
Once you've gotten this far, it's easy to add more layers.