Read the label. What says cotton or wool yarn may not be so much. Why is this important?
because if you are going to be dyeing or felting it makes all the difference. Of course I have learned the hard way. Just because it says alpaca doesn't necessarily mean that it is 100 percent. It may be 20 percent and the rest acrylic and that will not felt.
Same with the cottons just because it says it is cotton yarn it might be only 20 percent maybe less and the rest acrylic and if you are looking to dye either the cotton or wool you will be disappointed in the end. So once again read the label
There is a lot of work involved in wanting a felted item and quite disappointing to knit or crochet something, wash in hot water just waiting for the felting process and you pull it out and nothing magic has happened.
So when I am wanting to felt an item or dye my yarn I read those labels.