The initial lambda value measured just after spraying is lower than that stated in the property declaration. This is the so-called initial lambda, the magnitude of this parameter at a level from λ=0.033 W/(m.K) is obtained only shortly after application and can in no way be taken into account in the selection of the material. The change in lambda is due to the penetration of atmospheric air into the foam cells; once gas equilibrium is established, the lambda value remains constant.
The declaration of properties states the value of the declared (aging) lambda, which stabilizes after spraying and takes into account the maintenance of properties min. 25 years. In the case of Crossin foam, this value is λ= 0.037 W/(m.K).
Declared lambda is the only value that should be taken into account when trying to compare polyurethane foams offered on the market. Often, foam manufacturers or contractors, wanting to increase the value of their product, quote the initial lambda value. Such action is misleading the customer. Want to check the actual parameter one should ask for the Declaration of Performance and check the value of the declared lambda. The absence of the above document or the entry of declared lambda may raise doubts about the correct marketing of the product.