"Research indicates that the hot water extraction system provides the best capability for cleaning. This system is commonly referred to as "steam cleaning", although no steam is actually generated. The process consists of spraying a solution of water and detergent into the carpet pile and recovering the water and soil with a powerful vacuum into a holding tank. This can be done from a truck-mounted unit outside the home with only the hose and wand brought inside or by a portable system brought into the home.
It is to your advantage to use professional cleaners because their experience enables them to do a better job than you can do yourself. Their equipment has more extraction power than the rental units available to individuals, and the carpet should dry more quickly. True professionals also understand the equipment, know the proper cleaning agents for the situation at hand, and recognize the differences in fibers and carpet construction."
Shaw Industries Inc. (World's Largest Carpet Manufacturer)
"Ground-in soil can only be removed by professionals with high powered equipment.
Choose a professional company who uses a truck-mounted steam extraction system. These cleaners are usually more efficient, deliver a higher degree of soil removal, and reduce drying time."
World Carpets - Care and Cleaning Guide
"Steam Cleaning - is by far the most thorough on-location method for removing embedded soil. Since their is no rotary brush, there is minimum pile distortion: This is especially important in shags or plushes. Detergent build-up is minimized because of immediate vacuum pick-up."