Sizing for XL says 25.5". I doubted that and ordered it anyways, and my head is 23.25", and this hat just barely fits. I like my hats to cover the cold spot in the center of your forehead from the wind, and also to cover your ears. I had the dome from years ago, and it definitely had more room, but it was still too tight. around the head. This model with the windproof goretex is much lighter weight material, which means the seam that runs around your head is not thick and will not cause you a headache; and the redesign of how they sewed the top together, it now fits under my mountain bike helmet without having to get a larger one for the winter; and, I think the goretex has a much better look to it than the old fabric material. That said, it does not measure 25.5", but more about 23.5", and if you pull it down so it covers the coldspot in your forehead, which you know if you mountainbike in the cold, once that part of your head gets cold, you will generally get sick; so I keep it covered up, and switch out hats if the moisture from sweating and wicking starts to make it too cold. So, if you keep that part covered, then like the photos of the models, your ears peak out a bit in the bottom. So, after trying all the new hats from OR and mountain hardwear and north face, I would still have to choose this one. They could add about 1/4" more material to cover the ears, or they could just redesign the back of it to make it like the wind warrior hat from outdoor research, which has a nicer full coverage for the ears, and then it would be just perfect. I haven't put it through the winter test yet, I am expecting it to work as my other mountain hardwear dome hat which is the only hat I have ever needed from freezing to -20 in ohio, in the wind, in the rain, for everything from hiking to mountain biking to climbing.
