I have read about wool dryer ball in blogs and on Pinterest. I decided to put some together, since they are suppose to cut down on clothes drying time. I had some variegated wool yarn that I wasn't going to use for anything else. It took them a bit longer to felt than I had expected, but I finally got them to work.
I used them in my dryer and I wish I'd made them long before this. They really cut down on the dryer time. (Save $$$) I went down to throw something else in the dryer after a short period of time and found my load of laundry was almost completely dry. I have been using them for a month and I won't go back to using a dryer without them. The only downfall, is that they get in sleeves and pant legs, so you have to collect them when you fold laundry. If you only put one or two things in the dryer, it sounds like some enormous popcorn machine! I can live with both of those things.
I made six dryer balls with two small skeins of wool yarn. It doesn't matter what color they are, so you could buy a sale yarn. I encourage you to give it a try. There are tutorials on many blogs and Pinterest.