This is easily one of our most asked questions- usually right after we've asked if the customer wants their yarn wound! It turns out, there are a couple of reasons why...
First, a quick vocabulary lesson...
Hank or Skein - Unwound, usually straight from the hand dyer, in a large O that is then twisted on itself. Example: Blue Moon Fiber Arts Socks That Rock on the left and Malabrigo Rios on the right below. Hanks/skeins need to be wound before they can be knit or crocheted with.
Cake - Center-pull end result of a hank or skein after it's been wound on a ball winder. Example: center below.
Pull Skein - Pre-wound, center-pull, in a sort of log shape. Example: Berroco Comfort (not shown).
Ball - Pre-wound, donut-shaped, sometimes center-pull, sometimes not. Example: Berroco Arno and Jojoland Melody below.
The biggest reason yarn so often comes in hanks is that it travels much more reliably that way. Wound balls tend to snag, fall apart, and generally become tangled knots.
Also, leaving yarn unwound is usually better for the fiber for storage. When yarn is wound, it puts tension on the fiber. This is fine for a while, but left that way long-term it can slowly stretch the yarn. If you don't think you will get to the project for a few months or years, do yourself and your yarn a favor and hold off on winding!
Also importantly, it's often to see the color of yarn when it is unwound! Especially if it is hand-dyed, kettle-dyed, variegated, or speckled, you can unwind the skein and easily see it in all of its glory to help pick the perfect one for your project.
Finally, if the yarn is a hand-dyed yarn, cost factors in. Winding the hank into a ball after it is dyed is just one more step a dyer has to do and therefore pass the cost on to the customer. Leaving it as dyed in the skein keeps costs down for everyone!
THE BOTTOM LINE
While it's a little more work, leaving yarn unwound in a hank is better for it, and usually better for the dyer and you, too!