Something I’ve always wondered, and finally I’m asking. If when you knit you work off a ball of wool, why is wool sold in skeins and not in balls? I’m guessing it’s wound into balls to prevent tangling, but why not sell it that way to begin with?
Most yarn should not be balled up until it is ready for use, because it can get compressed or strretched on the ball. The hank keeps the yarn loose and springy.
The reason its wound into balls is that if you try to work off the hank, it will tangle into a mess. It can also be wound into a center-pull “cake” using a yarn swift and winder.
Commercial manufacturers have special machinery that can create a center-pull skein without it compressing the yarn. So you can in fact buy a skein of yarn that is designed to be worked off directly. As such equipment is expensive, you will usually see the twisted hank with smaller, artisan-type producers
Yes I was going to say, many, many skeins are made to be worked from and don’t have to be balled first. Only really loose skeins need to be wound before using.
Probably a minor consideration compared with what Hello and Claire said, but there’s also the issue that if you drop a ball of yarn, it’ll roll and unwind. That’s just something you deal with when you’ve got 2 or 3 balls in a basket by your rocking chair, but I could see it being a real problem in a store with racks piled with yarn.
Notwithstanding all that, I have seen yarn sold in balls occasionally. It’s usually specialized stuff (odd colors or the like) that you wouldn’t need to use very much of.
Very interesting! I wondered if it had something to do with stretching the yarn. Also interesting that there are skeins/hanks set up so they can be used without tangling.
Thanks for the info. It’s a small thing, but something I’d always wondered about.
Chronos: You need balls, though, so that the kitties can play with them. 
You probably didn’t intend for that last line to come out sounding quite that painful… <wince>
A commercially wound center-pull skein looks oblong, like this:
http://www.herrschners.com/220_img/012600P.jpg
There’s also a commercially wound center-pull ball, that looks like a doughnut, like this:
Then there’s a hand-wound ball, like this:
And a “cake,” a skein or hank that’s been wound on a winding device into a center-pull cylinder, like this:
http://www.freshstitches.com/wordpress/wp-content/uploads/2010/04/centerpull.JPG
BTW to corral your hand-wound balls you can get a yarn bowl or work the yarn from inside a project bag
