It's even brighter in real life. Like, it hurts my eyes in the sun light.

I used Loops and Threads soft classic in Neon Yellow. It's 2x2 rib and then I used the crown decreases described here. I also added an obnoxiously large pompom with most of the leftover yarn and tied a piece of yarn inside the hat so there's a loop to tie it to a coat (my sister sails a lot so this should prevent it from blowing away).