Aerogel 10mm thick.
You can buy it on eBay.
I applied it in a spiral wind with spray glue 3m 77.
Work outside up wind of your project.
It's really dusty stuff, but worth the effort.

ebay DOT com/itm/Aspen-Aerogel-SPACELOFT-Insulation-Hydrophobic-Mat-Per-Linear-Foot-10mm-/180860317203?pt=LH_DefaultDomain_0&hash=item2a1c1d 6e13

Steve

Hey,
Can you tell me more about the insulation you used for your hot water heater? How much did it cost? Where did you buy it? How did you attach it to the tank?
Thanks Mike