For such a simple design, choose an extra-special, soft and colourful yarn. I’ve knit the hat in 4 different yarns: the smallest shown is merino wool, the next largest is merino/camel, the next size is baby alpaca, and the largest is variegated suri-alpaca/merino/cashmere. Note that the fiber you choose may affect your gauge, which is why I’ve provided plenty of sizes.