From the pattern description:

Shirt is knitted in garter stitch and cotton yarn with a pattern in stockinette stitch and woolen yarn. The mixture of wool and cotton, as well as the design of the pattern, is related to the Bjuråker sweater on p. 51. Its checked garter-stitch pattern at the lower edge, where the white component is in cotton, led to these striped rectangular shapes. It is, of course, perfectly possible to knit Shirt exclusively in wool or cotton.