UPDATE 11/14/19Wore these during a half marathon, they felt lightweight and provided a perfect fitted cushion for each foot, with this being the first half marathon I have done at race pace where I didn't have any rubbing issues (toes, ankle, anywhere). These will absolutely be the tool of choice when running half and full marathons in the future. Still leaving at 4 out of 5 since they technically are a little "heavy" for "ultralight" socks, but they are as comfortable and supportive as any socks I have worn regardless of weight. Recommended, especially for anyone looking to "treat" their feet to a special pair of socks for intense events!.I wear an 11.5 shoe, and have been looking to treat myself to a new lightweight pair of socks for some upcoming races of half and full marathon distances. I have new shoes (Nike Vaporfly NEXT%, super lightweight and springy), and those rise up a bit more than I would like on the back of the ankle, so I needed to find a replacement for my current socks which were super low-rise.So based on reviews and the sizing chart, I decided to get the XL size. To be fair, the chart says Large is for up to size 11, and XL is for 12 and over; however, I read other reviews and other information that said to go with the larger size on these. They are wrong. The socks that arrived were waaaaay to big and the heel was riding up a solid inch above where it should. So I sent them back, and sure enough the Large size fits perfectly (and snug enough, although I honestly wish they were a little bit tighter).The comfort and feel is top notch. So far they seem to work well with my toes and pressure points, and probably will be a great decision for very long runs such as a marathon.But the reason I can't give them 5 stars is that they are supposedly ultralight, and even tenths of an ounce in the shoe area add up to lots of seconds or even a minute for a marathon type of distance. Well, I weighed them with a very accurate digital scale, and they come in at 1.5 ounces. That is light, sure. But sadly they are the heaviest running socks that I have, including my standard daily wear socks, which come in at 1.0 ounces. Even my thickest running socks from another brand are 1.3 ounces, so these are just slightly heavier. Part of that is due to the mid-rise design, which takes more material, and therefore will weigh more. I think the benefits of the design and support of this sock are worth it for very long distance races, so I am happy. But for a 10K or anything less where I want just pure speed, I will be looking for something lighter.Overall, recommended for endurance athletes that want a great sock and are not as weight obsessed as I am!