Felt is made by a process called wet felting where the natural wool fibres, stimulated by friction and lubricated by moisture (usually soapy water), move at a 90 degree angle towards the friction source and then away again, in effect making little "tacking" stitches. While at any given moment only 5% of the fibres are active, the process is continual, so different 'sets' of fibres become activated and then deactivated, thereby building up the cloth.
This "wet" process takes advantage of the inherent nature of wool and other animal hairs. The hairs are made up of unidirectional scales, and they are also naturally kinked. It is this combination which reacts to the friction of the felting process, forcing the scales on the hairs to lock together and thus causing the phenomenon of felting. It tends to work well with wool fibres because their scales, when aggravated, readily bond together.
It is also possible to produce artificial felts. If made using the wet method, an artificial felt will contain a minimum of 30% wool fibres with the rest being artificial fibres. This is the minimum composition necessary to hold a fabric together with the fibres alone; it would be difficult to form a stable fabric by hand below this ratio. Wholly artificial felts are actually needle-felts (see below).
An alternative felting process involves a steam roller rolling over the unwoven fibres in a shallow pool of water with the cloth rotating as the steam roller passes over it. This method is widely used in small towns in India where mass manufacturing of clothing is performed.
Needle felting is a popular fibre arts craft that creates felt without the use of water. Special needles that are used in industrial felting machines are used by the artist as a sculpting tool. While erroneously referred to as "barbed" needles, they in fact have notches along the shaft of the needle that grab the top layer of fibres and tangle them with the inner layers of fibres as the needle enters the wool. Since these notches face down towards the tip of the needle, they do not pull the fibres out as the needle exits the wool. Once tangled and compressed using the needle, the felt can be strong and used for creating jewelry or sculpture. Using a single needle or a small group of needles (2-5) in a hand-held tool, fine details can be achieved using this technique, and it is popular for 2D and 3D felted work.
From the mid-17th to 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 sliced off in thin shreds, the fleece coming away entirely. The fur was blown onto a cone-shaped colander, treated with hot water to consolidate it, the cone peeled off and passed through wet rollers to cause the fur to felt. These 'hoods' were then dyed and blocked to make hats. This toxic solution and the vapours it produced resulted in widespread cases of mercury poisoning among hatters, possibly giving rise to the expression "mad as a hatter".
Felt is used everywhere from the automotive industry, to musical instruments and home construction. It is often used as a damper. In the automotive industry, for example, it damps the vibrations between interior panels and also stops dirt entering into some ball/cup joints. Felt is used on the underside of a car bra to protect the body.
Many musical instruments use felt. On drum cymbal stands, it protects the cymbal from cracking and ensures a clean sound. It is used to wrap bass drum and timpani mallets. Felt is used extensively in pianos; for example, piano hammers are made of wool felt around a wooden core. The density and springiness of the felt is a major part of what creates a piano's tone. As the felt becomes grooved and "packed" with use and age, the tone suffers. Felt is placed under the piano keys on accordions to control touch and key noise; it is also used on the pallets to silence notes not sounded by preventing air flow.
A felt-covered board can be used in storytelling to small children. Small felt cutouts or figures of animals, people, or other objects will adhere to a felt board, and in the process of telling the story, the storyteller also acts it out on the board with the animals or people. Puppets can also be made with felt.
German artist Josef Beuys used felt in a number of works.
In the early part of the 20th century, felt hats, such as fedoras, trilbies and homburgs, were worn by many men in the western world.