From the designer’s website:

Easy shawl in garter stitch, no purling! Knitted in one direction and then another. Show off variegated yarn or use a solid color to emphasize the lines.

You may substitute any 3 to 5 sts to 1 inch/2.5 cm. yarn, but it might require more yardage. Suggested yarn is one example of a yarn that will knit to the recommended gauge.