3DFINS XS Recommended for Rail Work Training Future Fins 3D fins are quite soft, and if you step on them too hard, the fins won't work, making them great for rail work training. If you weigh under 55kg, you can ride them normally. Compared to the S size, there is clearly less fin resistance and more speed. For those weighing over 55kg, I think they are good for rail work training. Because they are soft, they are also recommended for women and children with weaker leg strength. (They are not soft fins.) Thank you for looking.