The density probably has to with weight of the yarn. Usually we suggest worsted weight, smooth, solid color for beginners. Generally the less expensive ones are used in learning.
See if there is any reference to the type or a name in the beginning or end of the book. Also check the original publishing date. If its older it's likely it's a now discontinued yarn.
The best thing you can do is go to a yarn store or a craft store like Joann, Michaels, Hobby Lobby...and just look at the yarns.