The Felting Process
In the wet felting process, hot water is applied to layers of animal hairs, while repeated agitation and compression causes the fibers to hook together or weave together into a single piece of fabric. Wrapping the properly arranged fiber in a sturdy, textured material, such as a bamboo mat or burlap, will speed up the felting process. The felted material may be finished by fulling.
Only certain types of fiber can be wet felted successfully. Most types of fleece, such as those taken from the alpaca or the Merino sheep, can be put through the wet felting process. One may also use mohair (goat), angora (rabbit), or hair from rodents such as beavers and muskrats. These types of fiber are covered in tiny scales, similar to the scales found on a strand of human hair. Heat, motion, and moisture of the fleece causes the scales to open, while agitating them causes them to latch onto each other, creating felt. There is an alternative theory that the fibers wind around each other during felting. Plant fibers and synthetic fibers will not wet felt.
In order to make multi-colored designs, felters conduct a two-step process in which they create pre-felts of specialized colors—these semi-completed sheets of colored felt can then be cut with a sharp implement (knife or scissors) and the distinctive colors placed next to each other as in making a mosaic. The felting process is then resumed and the edges of the fabric attach to each other as the felting process is completed. Shrdak carpets (Turkmenistan) use a form of this method wherein two pieces of contrasting color are cut out with the same pattern, the cut-outs are then switched, fitting one into the other, which makes a sharply defined and colorful patterned piece. In order to strengthen the joints of a mosaic style felt, feltmakers often add a backing layer of fleece that is felted along with the other components. Feltmakers can differ in their orientation to this added layer—where some will lay it on top of the design before felting and others will place the design on top of the strengthening layer.
The process of felting was adapted to the lifestyles of the different cultures in which it flourished. In Central Asia, it is common to conduct the rolling/friction process with the aid of a horse, donkey, or camel, which will pull the rolled felt until the process is complete. Alternately, a group of people in a line might roll the felt along, kicking it regularly with their feet. Further fulling can include throwing or slamming and working the edges with careful rolling. In Turkey, some baths had areas dedicated to feltmaking, making use of the steam and hot water that were already present for bathing.
Info sorced from wikipedia