We focused this study on the car because the car offered a small, easily-controlled environment where people sleep. As we toured cars in which people live and talked with owners, we wondered, how do they keep warm and how warm is it inside a car at night relative to the outside temperature? How much can we influence the temperature inside a car on the street at night using common insulating techniques that we learned from people who live in their cars? Using thermal mass? How much of a difference does warmth from a person make in the environment of a car parked on the street at overnight? Can we keep a compact car above 40 degrees overnight even when the outside temperature is below freezing?