The rating system is not very honest. They are factoring in appropriate clothing, not a hypothetical nude user. Individual metabolism is highly variable. Some people "sleep warm" while others do not. The pad is critical. I spent a sleepless night in an "Arctic"rated -15 bag, in the desert. I had only a groundcloth. The down fill was useless compressed. The next night I used sweaty horse blankets. I was warm, but smelly.The third night I made a bed of dried cowpies.