There is a wide range of insulation materials, including those based on minerals, such as mineral wool, various types of foamed plastics, and natural products such as cellulose. They are available in various forms including rigid boards, batts, loose (injected), and quilts, depending on the intended application.
How effective a particular material is at reducing heat flow is described by its thermal conductivity, or K-value. This is also known as the lambda (λ) value. The lower the K-value, the better the performance of the insulation material. The R-value (or ‘resistance’) indicates how good a material is at resisting the flow of heat at a certain thickness. The higher the R-value the better.
The inverse of the sum of the R-value for each layer of a building element is used to calculate the overall U-value. Adding an additional layer to a building element increases the overall R-value and reduces the U-value of the finished structure thereby improving energy efficiency.