The books have a "hinge" so they fold back and lay flat, which was great for practicing portraits, value scales, and eyes in our books. There are tons of instructions for books online, so if you're interested in making your own, it's easy to find a quick online tutorial for them.
One day when we had a crazy picture day schedule, we folded envelopes to glue inside their books. I plan to use these for sub days too, so they can work on them throughout the year.
They look so good in our display case!