I have been gone for a WHILE! So busy, with my daughter in school (which is making us all sick all the time- GRRRR), my baby, and my toddler- oh and making stuff! I've gotten a lot of diapers done, and a lot of nursing covers too. I even made a few sets of wool dryer balls too!
I will tell you how to make dryer balls now.
For each ball, you need about 50 grams of 100% wool yarn. Lion Brand Fisherman's (or something like that, you'll know it when you see it) wool works well.
Make a small ball (1" around or so) and sew the end of the yarn back into your little ball with a large holed yarn needle.
Repeat for as many balls as you need.
Put all the balls into the leg of a pair of tights you don't really like (or a knee-high, whatever!) and use non-wool yarn to separate the balls (tie between each one and at the end so the one at the open end doesn't fall out).
Then wash and dry them with a load of laundry, in tights as before or in a (tied shut) pillowcase- just not a white one, unless your yarn is white. And don't wash them with diapers (the lanolin in the wool can cause your diapers to repel- but you wouldn't do that anyway, would you? Common sense rules here- wash them in a load of not-so-dirty laundry!)
Then take them out and finish wrapping the yarn into (@50 gram each) balls.
Wash and dry them with another 2-3 loads of laundry.
Keep drying them with your laundry until there is no more sheep smell (another 2-3 dry cycles).
If there are any threads hanging off, cut them. Congratulations! They are ready to use!
Or you can buy some if that's too time consuming for you!