Wool is the yarn of choice for making dryer balls. These balls are meant to be used for the efficiency of laundering clothing. When placed in the washer, they bounce around and help loosen the dirt and soil in the items. When placed in the dryer, they bounce around and fluff up the items shortening the drying time.
Wool gives them some weight to do their job. (Acrylics don’t seem to work and also don’t felt.) When making them, use pure wool that will felt. Wind into a ball and then I use a felting tool to help process them. Soak the ball, use soap to clean the spinning oils out of them and assist in felting. Throw them into the washing machine and start the processing with your regular laundry. Wool yarn, because it is all different, may need a wash/felt processing a few times. Watch the magic!
The ones below have had some surface embellishment using the multiprong (7) felting tool. The tool can be purchased online from EBay.com or Ebay.ca for a buck or two.