After making several different types of dryer balls, I settled on this one as my favorite.

For each ball, I use about 1.75 to 2 ounces of wool for the core, to make a core of about 8.5 to 9” in circumference (wound pretty tightly).

The jackets each took about 10 grams of worsted-weight wool.

Notes:

After 1st increase: 20 sts
After 2nd increase: 30 sts
After 3rd increase: 40 sts

The pattern says to knit in stockinette until the total work is about 3.5” from the cast-on. I worked one purl row after row 5 (last increase row), and then 10 more rows in plain stockinette before doing the decrease rows to get to that size.

The jacket should be loose around the core, since it will shrink quite a bit in the felting process. However, it took 2 trips through the washer and dryer before the jacket really shrunk down enough to be snug over the core. I think if I make more of these, I’ll probably cast on 8 stitches instead of 10.

The bottom photo shows how much excess fabric there was in the jacket before felting.