What is felt used for?
Felt is a fabric made directly from wool or other hair fibers, or mixtures of these fibers with other natural or synthetic fibers, without spinning, weaving, or knitting. The loose fibers, which have a crimp and surface scales, interlock and compact when they are subjected to moisture, heat, agitation, and pressure, forming a dense cloth.
More than 150 different types of felt are produced for uses such as thermal insulation, sealing, soundproofing, shock damping, vibration isolation, cushioning, and packaging, and for hats, clothing, and trimming. It is made in many thicknesses, ranging from 0.08 to 7.6 cm, and in many weights, ranging from 3 ounces to 65 pounds per square yard (100 grams to 36 kg per sq meter).
Felt is one of the oldest types of fabrics. Caps of thick felt dating from the Bronze age in Europe are displayed in the National Museum in Copenhagen. References in Homer indicate that felt was used in Greece for slippers, pads, and capes by 1000 B.C. The floors and walls of the Kurgans (Scythian graves of the 5th century B.C.) in Russia were lined with felt. Special workshops for making felt hats and gloves were discovered in Pompeii.
For centuries felt was handmade by washing wool, spreading it out, moistening it with water or whey, and beating it with sticks, or rolling it in a blanket prior to pounding. Mass production of felt was made possible by the invention of the wool-carding machine in the mid-18th century and further implemented by the invention of the hardening machine in the mid-19th century.
In modern felt manufacture, raw wool or fur, or a mixture of these fibers with other fibers, is blended in a mixing or picking machine. It is then carded; carding arranges the fibers into a thin web. The gossamer webs are removed from the card and assembled in layers, forming a thick batt. The batt is then moistened and moved through a hardening machine. In a plate hardening machine, the batt is steamed and drawn onto a plate under a heavy, heated platen that vibrates in a horizontal plane as it presses the batt, forming the fabric. In roller hardening machines, the batts are pressed by rollers rather than by plates.
From the hardening machine the fabric (except cushioning and padding felt) is sent to a fulling mill, where it is shrunk up to 50% in both length and width. After fulling, the felt is washed and finished in several ways. Finishes include those designed to make the fabric water-repellent, flameproof, or mothproof. The final finish is calendering, or tentering, which stretches the fabric to shape while it dries.