I bought acoustic insulating foam from McMaster-Carr . . . but haven't had time to install it yet since I'm just finishing installing my new upholstery.
I ordered 8' of the 1 inch skinned adhesive-backed. It has the highest noise reduction coefficient. Specs say adhesive is good to 225 degrees.
2005 X2, Viper Red, MCX, OJ TZ-X5 prop, PPass, rear 750 sacs, KGB, IBS, Bennett Wake Plate, custom wake shaper
(previous) 2001 X5, 1991 TriStar 190