Hat #3 from the Head in the Clouds collection.

This entire hat is worked using fingering weight yarn held double. You could also use DK or light worsted weight yarn held single (you will need approximately 200-250 yards). To complete the sun hat you will need some additional materials beside yarn and needles. See below

Notions
Approx. 50” 19-gauge steel millinery wire
One plastic wire joiner for millinery wire
Size G/4.5mm crochet hook
Tapestry needle for weaving ends
36” of 3/4” to 1.5” ribbon (optional)
Fabric stiffening spray (optional)

You can purchase millinery wire and joiners here:
https://www.judithm.com/catalog/wire-joiners-boning