Through air drying (TAD) is a process in which hot air is forced through a wet, porous material by imposing a pressure differential across the material. As the air passes through the porous material, the air heats the material and supplies energy to evaportate water. The air leaves at a reduced temperature and increased water vapor concentration. It is the intimate contact between the hot air and the material, coupled with the large internal surface area of the porous material that gives the high drying rates and superior bulk qualities of paper. This process, however, often comes at the price of high energy consumption.