The yarn I used for this slouchy hat is 35% merino wool, 64% acrylic and 1% polyester, for needles No. 5 - 5.5.
Cast on 74 sts (choose your needle size). Work like this:
Rows 1 and 3 - *K2, P2, K6, P2*, repeat from * to * 5 times; K2.
Even rows - work sts as they appear: K knitted sts, and P purled sts, but K the first and the last sts.
Row 5 - *K2, P2, transfer next 3 sts onto an extra needle IN FRONT OF the piece, K3, put the 3 transferred sts back to the left needle and K them (= cable), P2*, repeat from * to * 5 times; K2.
Repeat row 1, and work the cable (from row 5) in every 9th row.
Make the desired length, then sew the sides together to form a tube. Gather one opening of the tube by sewing it by hand and your Schtrumpf Hat is done!