I've got the 949i Eskimo insulated pop up and it's warm inside with a buddy heater on low. Me and the girl Brought it up to the eel pout festival last year and camped in it all weekend long in t-shirts and were just fine. My buddy has one that's twice that size non insulated and with a sunflower heater on low your good to go with just a t-shirt on. I'm upgrading this year to the size he has, but going to special order the insulated version just because its the crap. Eskimo all the way bud.