ICS or batch collectors reduce heat loss by thermally insulating the tank. This is achieved by encasing the tank in a glass-topped box that allows heat from the sun to reach the water tank. The other walls of the box are thermally insulated, reducing convection and radiation. The box can also have a reflective surface on the inside. This reflects heat lost from the tank back towards the tank. In a simple way one could consider an ICS solar water heater as a water tank that has been enclosed in a type of 'oven' that retains heat from the sun as well as heat of the water in the tank. Using a box does not eliminate heat loss from the tank to the environment, but it largely reduces this loss.