The Cartesian Hat is knit with two colors using the two-color helix knitting method. It’s a companion to the Learn Something New: Helix Knitting article, along with the Cartesian Cowl pattern. The brim is worked in a simple cable pattern based on 2x2 rib and is continued into the body of the hat while working helical stripes. The striped pattern is continued during the crown shaping and, to finish the hat, an optional pompom can be added to the top.