The goal of being twice as productive with half the resources (materials and energy), leading to a factor 4 improvement in efficiency. Alternatively, practices which are just as productive with 1/4 of the resources or 4 times as effective with the same resources also count.
The concept was introduced in the 1998 book, Factor 4, written by L. Hunter Lovins and Amory Lovins of the Rocky Mountain Institute, and Ernst von Weizsäcker, founder of the Wuppertal Institute for Climate, Environment & Energy. The book explains how relatively easy it is for businesses to achieve these results with existing technologies. It has many examples of real-world projects that save money and reduce pollution simultaneously. Another way of phrasing the Factor 4 efficiency gain is that it reduces energy and materials usage by 75%.
While Factor Four is a common term representing a minimum four-fold increase, Factor Ten–ten times as much productivity from the same inputs (ranging to the same productivity with 1/10th the resources)–represents an even greater challenge. Factor Ten equates to a 90% decrease in resource usage.