Phase-Change-Materials (PCM) transition from solid to liquid state at a certain defined temperature; just as H20 transitions from ice to water. During the melting process the material can absorb large amounts of thermal energy without actually becoming measurably warmer. GLASSX uses Calciumchloridehexahydrate (CaCl2 6H2O), a nontoxic salt, whose melting point is precisely at room temperature. When the building interior in summer starts warming up beyond this temperature, the PCM melts and absorbs the thermal energy that would lead to overheating otherwise. As the element is positioned in (or closely behind) the façade, the PCM absorbs not only the internal heat loads by convection but also the external solar energy input.

This permits a far higher absorption rate compared to PCM placed in walls or ceilings. The translucent PCM transmits most visible light but absorbs infrared radiation completely. After 8 hours, when the PCM is entirely molten the outside temperature usually already decrease below the melting point and the material starts recrystallizing in the cooler night air. Until the next morning, the PCM will be solidified completely so the cycle can begin again.