I coach age group swim and got this to help the swimmers who have too wide a kick. It is an '8' shaped elastic band. I had imagined it was going to be rubber, I don't know why. Looking at it I didn't think it would yield great results but it has been helpful. Only problem is with such a variety of kids using it, it stretched out very quickly (in two weeks). So while it was snug on the thighs for the first couple of swimmers, once the bigger kids had used it, it was too loose on those with smaller thighs (age group 11-15). I would recommend it for one swimmer who is using it for themselves. And for my purposes, I would get a couple had keep them marked for size. Even though they come in the same size, I would mark them S,M,L and give them to the kids accordingly by their size so the band stayed fitted. As to function, for those with strong legs and kick it worked better because they worked against the band, which you have to do. For those with weak legs, their kick became more fly like as they had trouble separating their legs. However, I found this a good drill for developing stronger quads and glutes for them. So I would recommend this product.