The bobbles are worked two different ways. You have the traditional bobble. I took a little spin on the traditional bobble to use 5 unworked treble crochets, to create the extended bobble, which made this row have a ruffle effect to the middle of the beanie.

You can use the yarn I used for this pattern or you can use different types of worsted weight yarn. You can change your colors like I have or just keep it in one solid color.