I found the Jennifer Maker blog today. Her page on the best types of paper for different crafts goes into a lot of useful detail and is worth a read, but I found her summary table useful as a quick reference guide.
All yarn for knitting or crocheting is made from natural or synthetic fibers. Different types have different qualities – some good, some not so good. These can also be blended by manufacturers to offset an undesirable characteristic – such as itchiness – as much as I love pure wool I can’t wear it. I’ve tried to put together some of the most common.