Go for the hot air. The energy needed to heat and blow air at your hands is far less than the energy needed to make and transport paper towels and haul waste away. One US study found that nine fully grown trees are cut down to supply an average fast-food restaurant with paper towels then create over a year; the tossed towels then create over 450 kilograms of landfill waste. The hand dryer is also more hygienic. Doctors at the University of Ottawa claim the hot air gets into more crevices in the skin,killing of germs quicker.