This tutorial shows how to make a yarn puffball (a.k.a. pom-pon). I believe this method is more sophisticated than the other methods I've found online. It produces more durable puffs that can be attached temporarily or permanently.
Step 1: Items You'll Need:
1. Yarn (between 150 and 200 yards)
2. 30" Crochet thread (I think this is size 8 but I'm not positive. For this application, the bigger the better, we need it to be strong.)
3. Empty soda can
4. Darning needle
Step 2: Wrap the Yarn Around the Can
1. Tie an overhand knot
2. Tighten the knot on the can
3. Wrap the yarn around the can. I made 225 wraps for this puffball.
Step 3: Prepare a Constrictor Knot
Using the crochet thread, prepare a constrictor knot approximately 3" in diameter. You'll use this knot to bind the loop in the next step.
The diagrams below show how to tie a constrictor know using paracord so that it is easy to see.
Step 4: Tighten Constrictor Knot Around Yarn Coil
1. Slide the coil of yarn off the can.
2. Slip the constrictor knot around the coil of yarn.
3. Pull the knot tight. The tighter the better (as long as you don't snap the thread). If the thread snaps, simply cut it off and use a new piece of thread. The great thing about using a constrictor knot here is that once tight, the knot will not loosen.
4. Tie a simple overhand knot secure the knot. (Just to be complete, an overhand knot is the first knot you tie when you are tying your shoe, before you tie the bow.)
Step 5: Cut Open and Trim the Puffball
1. Hold onto the thread and cut around the coil. Once you've cut all the way around it should look like photo #2.
2. Trim the excess yarn until it is shaped like a sphere. This much yarn will produce a nicely shaped ball approximately 3.5" in diameter (see picture #4) but you can also trim it down to 2.5" (see picture #5).
Step 6: Sew the Puff to the Hat
Using the darning needle, pull each end of the thread through the top of the hat.
If you want the puff attached permanently, simply tie a ligature knot (often called a surgeons knot). The nice thing about the ligature knot is that after you tie the first part (the double overhand knot) you can tighten the knot and it won't loosen easily. You want the pull the knot pretty tight so that the puff isn't floppy.
If you want to be able to remove the puff, move on to the next step.
Step 7: Tie the Puff on With a Parcel Knot
1. The first step in tying a parcel knot is tying a bow (just like the kind you use to tie your shoe).
2. Pull one of the loops through the other loop (photo #1 and #6).
3. Holding the inner loop, pull the long end to tighten the outer loop onto the inner loop (see photo #3).
Note, once the knot is tied, it is difficult to untie the knot simply by pulling the free ends. To untie the knot eaisly, first pull apart the loop and the alternate free end (see photo #4). Then let go of the loop and continue pulling on the end to untie the knot.
Step 8: Finished
You are done! Congratulations.