Imagine a bath of water at lets say 50 degrees C,and it cools to 40 degrees C in 10 minutes. If the underside of the bath isvery well insulated, then would the bath cool more quickly, or slower?
heat would be lost by two processes. Convection of warm air from the water surface and radiation from both the surface of the water and the outside of the bath. If you insulate the underside it will stay warmer longer.Just think of the difference in rate of cooling between coffee in a china mug and a polystyrene container.