I have some plastic dryer balls. They look a little like a cross between a porcupine and a racquetball. My mom bought them for me several years ago when we started having trouble with our dryer. The purpose of the dryer balls is to help the clothes tumble and therefore, dry faster. I haven't done any scientific experiments, but they seem to cut down slightly on the dry times of large loads.
Once upon a time I had 4 dryer balls but one of them split open. I'm thinking it had some sort of defect in the plastic. Mrblocko's sweatshirt sleeves also like to eat them. I don't know why I never notice it when I'm hanging them up, or even think to look inside them when I'm doing a second load of laundry and all the dryer balls are MIA.
Anyhow, I saw this tutorial for wool dryer balls from Good Mama and thought it would be a fun thing to try. I got two dryer balls from one skein of 100% wool yarn from Joann Fabrics. I can't remember what brand, just that it was half off at the time.
All you really need to do is wrap the yarn into a small ball.
Then you stick the dryer balls in a sock or nylon of some sort, knotting the sock in between each ball. I used a holey old knee high sock and was able to easily fit two of them in there. If you don't stick them in some sort of sock, they will unravel before the yarn gets a chance to felt together.
I tossed this weird looking sock in with the HOT washes, like whites and towels. I would say it was about a total of four washes and drys. I had to spread this out over two weeks as we are a small family who only does three loads of laundry a week.
Once the balls have been through the wash and dryer for a few times, add second layer.
Here is what they look like after the final felting. (The blue spiky thing is one of my plastic dryer balls.)
This project took me several weeks to finish simply because we don't do a lot of laundry in our house, but over all it was one of the easiest craft projects I've done in a long time.
P.S. I bet these would also make great cat toys, provided you don't have old man cats like me.