I'll start using this in early Oct. for five day or longer bp trips, making sure I have enough clothing and food, temps by then would be in the 20's. Temps here in CA can get below zero F. Just keep a stove running in the AM to use as a hand warmer. Had the pack out for the first time this last weekend, using my WM Apache 15F bag, booties and my winter tent, no extra ccf pad under the new XTherm. Only 28F Sunday AM.