Another interesting application can be found in the company GlassX. In the inner part of two glass panes, PCM has been filled. The resulting product behaves as if it was a well-isolated, massive wall, however, it still has the characteristics of glass. In solid state, the PCM is coloured white whereas in the liquid state it is transparent. With this properties, the heat input can be controlled by the sun. Only when the PCM is molten light comes into the room and heats it up.