What insulation value do polycarbonate sheets offer?

The Ug-value (formerly called the K-value) indicates how much heat is transmitted through the sheet. In order to have a material that keeps the heat in as well as possible in winter, this value should be as low as possible. The insulation value of polycarbonate sheets is largely dependent on the geometry of the sheets. Solid polycarbonate sheets have about the same Ug-values as glass of the same thickness. Multi-wall sheets offer improved Ug-values down to 1.4 W/m_.K (Watt per square meter and Kelvin). The best results are obtained with multi-wall sheets that have a lot of intermediate layers, or intricate geometric structures. On the other hand, during summer one might be looking for a material that keeps the heat out as much as possible. In this respect one looks at the shading coefficient (SC), the visible light transmission (Tvis) and the solar energy transmission (Rsol). Ideally, one looks for a material that lets the light pass through (high Tvis), but keeps out the heat of the sunlight (low Rsol and low SC). The ratio between these two opposite properties is expressed as the selectivity index: a high selectivity index means a lot of visible light, but little heat passing through the sheets. All suppliers have special types of polycarbonate sheets that offer improved heat reflection during summer. The combination of good insulation both during summer and winter give these types of multi-wall sheets unique properties.