I had 3 skeins of each color and ended up with a dozen balls. In order for the balls to felt, you need to use 100% wool. I had some other yarn I was going to use that said it was wool but upon reading the label, it was 80% wool, not good enough. It has to be 100% wool. After I wound the balls, I used a needle to thread the ends into the balls.
I boiled the balls for 10 minutes to help the felting process begin. Then I put the water and hose with the balls into the washing machine and washed them on the hottest setting and dried them. I did this twice before using them. Some of the blue from the hose bled onto the balls but it hasn't affected clothes dried with them.
This is what they looked like after they were done. 3 of the balls were in the dryer being used when I took the picture. I typically use 6 balls in the dryer and it has definitely has cut the drying time. The dryer we have been using in the kitchen used to have to run 2 times before the clothes were dried but now they are done with one drying cycle. So happy to be saving electricity and money.
One thing I learned is not to wind the balls neatly like you would for knitting or crocheting. Wrap it but go all different directions forming the ball. I had a couple that I had to trim because a portion (it looked like a cap) fell off from the ball. Those balls were fine and usable after I trimmed them. I'm thinking if you spent more and got super good quality wool yarn they would felt better than mine have, but that said, they have worked well and will felt more with each use in the dryer. In my case, it is good to have a dozen balls because a ball or two goes missing when my kids do their laundry. Eventually they make it back to the dryer.