This second definition of NER also gives the rate of reduction of the annualized life cycle energy use. Any reduction in AEE higher than the associated increase in AEU (NER >1) would represent a decrease in ALCE and a life cycle energy saving. A reduction of AEE that does not represent a increase in AEU would have a NER of infinity and would always be a preferred choice from a life cycle energy perspective. An example would be when choosing between different insulation materials with similar performance and durability characteristics but different embodied energy as discussed by different authors [56–58].