From Schoolhouse Press:

Meg Swansen calls Debbie New “…arguably the most inventive knitting designer of this generation.” The Klein Bottle Hat is a perfect example - Debbie turns a complex mathematical abstraction into an arrestingly cute hat. Includes clear directions for two versions (of the many Debbie has developed over the years): one in ribbing and one in Garter stitch, each with unique construction. Also featured is the 3-handle variation of the Ribbed hat. Surprise yourself with the creation of this iconic mathematical image!

Print version comes in a 3-hole, archival quality sheet protector.