This simple knit cap uses a self striping yarn called Adriafil Spillo from Plymouth Yarns. Because the yarn is no longer available, you can use any bulky weight yarn that has some stretch to it. The Spillo yarn was listed at a bulky yarn, using US 10 needles. But I found that it was fairly think for bulky weight and knit up very light and airy. I would not recommend a stiff wool for this hat, this pattern and it’s gauge is meant to produce a stretchy lightweight hat.