Wool knitting yarn will often be sold in the form of a wrapped up spool or ball, or sometimes in a yarn cone. This method of storage, prior to purchase, allows you (the knitter) to easily keep it together, so that it is not all unraveled all over the place. Some may prefer to buy their wool knitting yarn on a cone, as it may stay wrapped up better with the cone in the middle. It gives the yarn something to be wrapped around, so even if it comes unraveled it can easily be wrapped back around the cone. These cones can also be used on a yarn knitting machine, if that’s your preferred method of knitting.
The yarn that is sold without the cone will usually have a sticker wrapped around it to hold it all together. Once that sticker is cut or torn off, the yarn becomes free of any hold, which can cause it to unravel as well. So you’ll need to find a way to keep it from getting tangled and turning into a mess once you open the pack of yarn, or tear of the sticker hold off of it.
Wool knitting yarn is also sold in a huge variety of colors and thickness. You can often find more descriptions of the yarn from the retailer, to include percentage of wool and other fabrics used in the yarn. Wool knitting yarn isn’t always made exclusively out of wool, but will be a combination of fabrics or textures.