I purchased this from a trail running shop for around 4000 yen as a preventative measure for plantar fasciitis. I've used it a couple of times, but I no longer have a need for it, so I'm selling it. My shoe size is 27 cm, but it felt a bit tight, so it might fit someone with a shoe size of 26 to 26.5 cm better. I use it with socks, and I found that it provides a significant arch support effect, unlike other supports. Here are the product details: ↓ FS6 Performance Foot Sleeve Ankle Support [OS1st] About OS1st: Among various supports, OS1st supports are used to prevent recurrence rather than during the acute phase, without putting excessive strain on the movement. Unlike rigid fixation devices used in the acute phase, they are breathable, easy to move in, and convenient to carry. They are classified in the "Next To Skin" support category and are the number one brand in the United States. The FS6 Foot Sleeve is used especially for conditions such as plantar fasciitis and Achilles tendinitis, and is the most popular support among OS1st products. It is effective in suppressing inflammation by compressing the inflamed areas of both plantar fasciitis and Achilles tendinitis. Another benefit of compression is that it addresses "splayfoot," which is one of the causes of fallen arches. Wearing the FS6 foot sleeve provides more stability to the midfoot than being barefoot, preventing the arch from collapsing. It is also recommended for those with bunions, as the moderate compression on the midfoot helps align the toes. Size: Generally, women should be fine with size S, and men with size M. Those with wider feet or high insteps may find that going up one size will fit. Please refer to the size chart in the image. Finally, if you feel the compression is too strong, avoid using it for extended periods and take it off periodically. It is also recommended to remove it before sleeping. The recommended time to wear it is from after returning home to before going to bed, and for recovery after running, etc. It is also recommended to use it with sandals that allow your toes to spread out fully.