At 4°C, I built an overnight camp beneath an uprooted spruce and slept there barefoot. Before dark, I needed a roof, an insulated bed and enough firewood to make the shelter work through the night.
The root wall reflected more heat than I expected. During the night, however, I discovered that my fire was larger than the shelter needed and had to adjust it. This video follows the shelter build, bed, fire, meal, overnight test and honest morning result.