firsts I would like to say that the communication from the company is excellenth, speed of response, answering questions and even trying to find solutions for your when your are not sure, the product itself is very good, the material is very sturdy, it allows for good grip and it slides nicely when rolling it, the material chosen is rubber which I think is a very good choice, also it is a very good size, so it can fit the size of different feet, big or small, in the middle it is slightly raised which helps it slide better in the arch of the foot, the only reason I gave a 4 star is because of a very small cosmetic issue on the , rubber materials that is due to manufacturing, but it is very small issue, this is not stopping me from ordering a batch. thank you