I use Ice Kings by Lacross rated for -100 and I still get cold. What I did was put one hand warmer in the tip of each boot so my toes are on top of it and now I can sit for a long time with no problem. I hunt in the Up of Michigan so it gets quite cold here and the toes are the first thing to get me out of the stand not anymore. It does help having the Ice Kings due to the extra room inside the boots to fit the hand warmers. I use 4 every day I go out, 2 for the feet and 2 for the hands and they last for 10 hours, perfect for one days hunt in the winter!!!