My mashes are all over the place. I have been mashing in a 10 gallon rectangular cooler that I added a simple manifold to. I recently did a test that showed a 10 degree drop in temperature over 60 min. This is way too high, since I don't want to add hot water to adjust part way through.
I noticed when I did this test that the tun lid got quite warm. Upon further investigation, the lid is totally un-insulated.
My first inclination was to get some styrofoam, cut it to fit the inside of the lid, and then line it with plastic. Instead I used "Great Stuff", cut it down with a hand saw after it dried for weeks, and tried to seal some foil over the top with silicone.
This setup lowers my temperature drop to 2 degrees per hour, which amazes me and it's just what I want. However, don't do what I did. Just get a thick sheet of styrofoam and use 2 sided tape to attach it to the inside of the lid. Then cover that with heavy duty foil and possibly some more waterproof 2 sided urethane tape to hold it on.
I used white silicone that did not dry correctly, then covered it with packing tape. It's a hack job. Also, Great Stuff fumes a lot as it cures. So don't copy (exactly) what I did.
