From the book, p 107:

Cables and dropped stitches come together for a fun and quick project suitable for spinners of any skill. The extra loft of the bulky two-ply fills the spaces of the dropped stitches and traps more air in the yarn, resulting in a warmer hat with less weight. The drumcarded fiber spun with a supported long backward draw made soft, airy singles. Kristi Schueler preserved the color layers in the batts by tearing the batt into a continuous roving.