3.Flatness: Steel Panel is composed by two steel plates. Since steel sheet is elastic and deflection will occur in case of distortion, so the flatness is max at 0.5mm; Calcium Silicate Panel will get distortion after long-term use by the cause of high thermal expansivity; While, as for Calcium Sulfate panel, since crystallization will create micropores all around, when temperature and humidity influence, it still can keep good stability. After processing, the flatness can reach 0.2mm and stability can keep it flat permanently.