I am a Mechanical Insulator by trade and i think the fastest, easiest, and the most efficient would be armaflex.. Its Mold resistant and flexible
and it made with Microban antimicrobial product protection provides added defense against mold on the insulation. Its mostly used for keeping things cold think of a beer cozy but it works up to 220 and higher so for a mash tun it would be ideal. I use it for everything that need to be regulated temp wise.
Thats my 2 cents