Increasing resource productivity by the X factor describes sustainable development. In house building, for example, the X factor stands for particularly climate- and resource-friendly construction. The entire life cycle of the house is taken into account.
Harburg21. (n.d.). X-Faktor. Klimaportal der Lokalen Agenda 21 im Raum Harburg. Retrieved 12 07, 2020, from https://www.harburg21.de/de/klima/klima-abc/x/
faktor X agentur. (n.d.). Info. faktor X agentur. Retrieved 12 07, 2020, from https://www.faktor-x.info/