Here on earth, the sun delivers much bounce, and the atmosphere surrounds it with a wall that reflects the energy back in. In outer space, however, there’s nothing — a vacuum — and the bounce all disappears very quickly, leaving very little moving. Lack of motion means little heat, and almost no transfer — very cold. Closer to home, if you wrap your hot coffee in a thermos — a hollow cylinder with all the air sucked out of it — there’s also very little in the way of excitable particles to move the energy from your hot coffee to the cold air around it. Your coffee stays hot.