Extending the lifetime of durable goods is an important aspect of the struggle for a sustainable economy. Indeed, extending the lifetime of goods will probably cause a decrease in the use of depletable resources. Therefore, it is important to analyse the forces that influence lifetime. For a general description of the relation between sustainability, depletion speed of resources and interest rates, see Heijman (1991). In their work, BohmBawerk and other Austrians provided an explanation for capital and interest. These insights can be extended to account for changes in the lifetimes of durable goods. It has to be stressed that the classical Austrian theory o f interest will be used here and not the slightly different modern Austrian version as has been put forward by, amongst others, Faber and Bernholz (see Zuidema 1993).