I use a 10 gallon Rubbermaid cooler mash tun for mashing five gallon batches, and I've had it for a very long time. I'm not sure whether the insulation is wearing out, or there is some other factor, but it no longer seems to hold heat as efficiently as it used to. The temperature can drop as much as 7 or 8 F over 1-1/4 - 1-1/2 hours of mashing. I keep the mash tun tightly wrapped with blankets during the mash. I also pre-heat the mash tun. I'm interested to know if others have creative ideas for maintaining a more steady temperature while using a 10 gallon cooler mash tun?