A center-pull ball of yarn lets you pull yarn from the center rather than the outside.
I love them because the yarn slides out easily, they don't roll around, and don't tangle when I'm knitting intarsia and have several balls on the go.
How to make a center-pull ball
You can make any ball of yarn into a center-pull ball. The main difficulty is getting hold of the end that's in the middle of the ball.
1. Delve into the ball to find the end. Sometimes you will find it easily, but other times you may have to pull out a clump of yarn from the center of the ball. This is affectionately known as a "yarn barf".
2. You can fix a yarn barf by winding a miniature center-pull ball (see below for how to do that) and putting it back into the ball.
How to wind a center-pull ball
This method doesn't require any tools and works for practically any length of yarn.
1. The most important thing is not to let go of the tail of the yarn. Wrap it around your little finger and trap it securely in your palm.
2. Now, start winding the yarn loosely around your index finger—for about 10 turns.
3. Slip the loops off your finger, keeping them together as much as you can. If the yarn doesn't come off easily then try again, winding more loosely.
4. Wind the yarn across the loops a few times, keeping it loose.
5. Keep winding at different angles, in a way that keeps the ball roughly spherical.
6. Once the ball is large enough, I like to turn the ball, rather than change the angle that I'm wrapping the yarn. I find it produces a neater result.
7. When you have worked through all the yarn that came out, tuck it back into the original ball with the tail poking out at the top.
8. If you're winding a complete ball, as opposed to fixing a yarn barf, then tuck the outer end underneath some of the strands to secure it.
If you find a bare spot on your Christmas tree, just whip up some center-pull balls in festive colors. Stash a pair of needles in the branches and you'll have emergency knitting to hand until January!