Thermal Values Explained
The primary measure of performance comparison amongst insulation products is lambda value (also known as K-value). The lambda value measures the thermal conductivity of a product as heat loss in watts (W) per metre Kelvin (K), expressed as W/mK. Simply, the lower the value the poorer the conductor of heat the better the insulating properties. Celotex products are up to 100% more effective than glass wool products.
R-value is a measure of thermal resistance, and is expressed as square-metre Kelvin per watt or m2 K/W. They are a similar performance measure to lambda value but take account of product thickness. With R-value the higher the value the better the resistivity of heat loss the better the insulator. The sum of the R–values of individual products combine to generate a U-value for the combined building element.
A U-value is a measure of how well building elements conduct heat. This is the primary measure which is used within the construction when selecting products and design elements. The calculation considers the amount of heat lost in watts (W) per square metre of material when the temperature is one degree Kelvin (K) lower outside. The result is expressed as W/m2K and the lower the value the better the insulating properties.
Please visit our U-value Calculator if you would like to determine the insulating properties of your construction.