Had another version of the flex-fit that wore out in the head area and was slightly more larger. Turned out to be an imitation brand.

These are the legit hats, you can tell my the branding and hat structure. I normally wear a large, but lately i'v been fading my hair or short. Grabbed a medium and it fits perfect if you use short hair styles. Has enough grip that it stays on but doesnt latch onto the head and can be used for hours. If you have longer, thicker hair or curly its probably safe to go large. I'm an adult, with an average looking head. So in my situation I could drop down to medium and still have slight room, but holds onto the head without being to loose. Which is the look/style I like.