I have tried the vest only once so far, since it is not that warm every day yet, here in NC. Aveline goes on hikes and walks, and she is heat sensitive. I did notice a big difference. and am very happy with the result. The vest is a bit big, but the smaller one did not fit over her big head. I had those vests before for my other Frenchie and my Boston Terrier, both also avid hikers. Big help for heat sensitive dogs on summer walks/hikes!