Yarn is used double throughout.

Each pattern has a different set of recommended yarns. The following is from the King Cole version.

Materials
Double Knitting
Superwash Wool (machine washable), Tristar, Pretty Lady, Carelon, Speedy, Crepe Romance, Gren Nylon, or Pixie Baby Nylon
13 balls
Quickerknit Pixie Nylon
10 balls.