How does single glazed Low E glass provide insulation?

The fact that there is a Low E coating on one surface of the glass, glazed to the inside, means that the glass will have a lower U value and hence provide better levels of insulation than normal clear glass. This is because the coating reflects the heat back into the room whereas glass without a Low E coating would allow the heat from the room to pass through it. A good example of this is 6.38mm ComfortPlus™ which has a U value of 3.6 compared to a 6mm clear float glass which has a U value of 5.8, an improvement of over 39%.