The lower the embodied energy of an insulating product, the lower its overall environmental impact and the faster its environmental payback will be. The environmental payback for an insulating product occurs when it has effectively conserved more energy by restricting heat loss or gain, than its initial embodied energy figure.
In the case of insulating products in energy saving applications the environmental payback period is generally extremely short, compared with the lifetime of the application. After the environmental payback is complete, the insulating products can go on saving energy for many years more. Because of this, the energy saved over the lifetime of an application is mostly far greater than the embodied energy of the insulating products saving that energy. Embodied energy is therefore usually irrelevant in the specification of insulating products.
In comparing the embodied energies of materials, the concept of a functional unit must be taken into account. In the case of ductwork insulation, the functional unit depends upon firstly, the density of the insulation and secondly, the thickness of insulation required to achieve a defined heat loss / gain. This thickness will vary depending upon the thermal conductivity (λ-value) of the insulation material. Thickness and thermal conductivity are used in calculation of the material thermal resistance (R-value) of the insulant, by dividing its thickness by its thermal conductivity.