177. If metal is a conductor of heat, why is it that aluminum foil will insulate food and reflect heat?
Aluminum may be a good conductor of heat, but its a terrible emitter or absorber of thermal radiation. When you wrap food in aluminum foil, you dramatically reduce that food's ability to lose heat via radiation if it's hotter than its surroundings or its ability to gain heat via radiation if it's colder than its surroundings. Aluminum foil doesn't have much effect on heat transferred to or from the food via conduction or convection because aluminum itself is a good conductor of heat.