To felt wool, use100 percent wool material, wash it using detergent and hot water in a washer till it becomes thick and full, and take the fuzz balls off it. Dry the material thoroughly, and use it as desired.
Before felting a woolen garment such as a sweater, check its label. Sweaters with labels that read 'super washed wool' or 'washable' cannot be felted.
Place the sweater inside a pillow cover, twist the cover's top portion, and fold it over about 5 inches. Secure the portion tightly using a rubber band. Place the pillow cover containing the sweater in a washer, set it to the highest agitation setting, and wash using 1/8 cup of detergent and hot water.
Switch off the washer when the wash cycle of the machine is completed. Remove the sweater from within the pillow cover, and check to be sure it has shrunk. The sweater's weave should be less obvious, and the material must feel full and thick. Wash the sweater in a similar manner till it becomes half its initial size. Then rinse the sweater in the washer.
Take the fuzz balls off the sweater by hand, and tumble dry the material in the washer using high heat. When the sweater is completely dry, remove any remaining fuzz balls to make the sweater's surface smooth.
The wool is now felted and ready to use for the desired project.