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.
Needle felting is a method of creating felted objects without using water. The special needles used to make 3D sculpture, jewelry, adornments and 2D art have notches along the shaft of the needle that catch fibers and tangle them with other fibers to produce felt. These notches are sometimes erroneously called "barbs", but barbs are protrusion (like barbed wire) and that would be difficult to thrust in to the wool and nearly impossible to pull out. There are many sizes and types of notched needles for different uses while working. Needle felting is used in industrial processes as well as in individual crafting.
Invented in the mid 17th century and used until the mid-20th centuries, a process called "carroting" was used in the manufacture of good quality felt for making men's hats. Beaver, rabbit or hare skins were treated with a dilute solution of the mercury compound mercuric nitrate. The skins were dried in an oven where the thin fur at the sides turned orange, the colour of carrots. Pelts were stretched over a bar in a cutting machine, and the skin was sliced off in thin shreds, with the fleece coming away entirely. The fur was blown onto a cone-shaped colander and then treated with hot water to consolidate it.The cone then peeled off and passed through wet rollers to cause the fur to felt. These 'hoods' were then dyed and blocked to make hats. The toxic solutions from the carrot and the vapours it produced resulted in widespread cases of mercury poisoning among hatters. This is the origin of the phrase "mad as a hatter" which was used to humorous effect by Lewis Carroll in the chapter "A Mad Tea Party" (Alice in Wonderland)