Different fabrics trap heat at different rates. You wrap conical flasks of hot water in five materials — cotton, flannel, polyester, wool, and Gore-Tex — and leave one flask unwrapped as the control. Each starts at 60°C. Checking the temperature every 30 minutes for two hours shows which fabric holds warmth the longest and is therefore the best at slowing heat loss.

Different fabrics trap heat in different ways, and some hold warmth far longer than others. You wrap conical flasks of hot water in five fabrics — cotton, flannel, polyester, wool, and Gore-Tex — leaving one flask unwrapped as a control. Each flask starts at 60°C. Every 30 minutes for two hours, you check the temperature. The fabric that keeps the water warmest the longest is the best insulator for cold weather.