If you have stayed at a hotel recently, you have seen a card in the bathroom exhorting you to help the planet by reusing your towels, thus reducing the amount of water, energy and detergent used by the hotel. Such appeals are typically based on guilt - you reuse the towels and the hotel receives the financial benefit.
The success of such efforts, however, is tenuous because it is entirely contingent on the convenience and good will of the guests.
Westin Hotels, however, have harnessed the free market to find a better way.
