Here’s what I know. Felt is a mass of dense wool and/or fur. It is not woven, but rather pressed and manipulated in a centuries-old process using heat, moisture and pressure or agitation. The result is the strongest, smoothest, most water-resistant natural fabric known. Soap helps in the felting process. Heat and moisture cause the outer overlapping scales along the wool fiber to open, and the soap allows the fibers to slide easily over one another, thereby causing them to become entangled. Wool fibers are made up of a protein called keratin. The keratin in the fibers becomes chemically bound to the protein of the other fibers resulting in a permanent bond between the fibers. The felting process is irreversible. Sometimes this is unfortunate if you are like me and have several unintentional child-sized sweater casualties on hand as silent reminders.
Since wool felt is not woven and doesn’t require a loom for its production, it can be made rather easily. Because of this, felt is the earliest known form of fabric. The true origin of felt is unknown, though I am aware of several cultures that take credit for the discovery of felt. One Sumerian legend tells of Saint Clement, a wandering monk, who cleverly wrapped flax fibers between his shoes and feet to prevent blisters. Upon arrival at his destination, he removed his shoes and discovered that the flax had, in fact, felted due to the heat, pressure and perspiration. Saint Clement became the patron saint for hat makers.
The steps included in making felt have changed little over time. Felted fabric is produced using heat, moisture and pressure to mat and interlock the fibers. While machinery can be used today to accomplish many of these tasks, the processing requirements remain unchanged. One exception is that until the late nineteenth century mercury was used in the processing of felt for hatmaking. Mercury was discovered to have debilitating effects on the hatter, causing a type of poisoning that led to tremors, hallucinations and other psychotic symptoms—hence the term “mad hatter.”
What makes a good sweater to felt? When looking for a thrifted sweater or two to upcycle for a felting project, I usually choose 100% wool. Other animal fibers will work as well—mohair, cashmere, alpaca, etc. Be sure the tag is not labeled “superwash,” since this “washable wool” will have been chemically treated to avoid shrinkage (felting). Remove all buttons, ribbons, labels, etc. from the sweater, cut it apart at the seams (completely cutting away the seams), and throw it in the hot-water wash and cold-water rinse with the (relentless) laundry pile. Often, I wash and dry twice.
Felt made with a thrifted sweater has all the benefits of wool—stability, durability, earthy texture—and has the eco-friendly attributes of being natural and second-hand. Hurrah!