I have a black shepherd cross puppy, and ive already noticed on warm spring days how quickly she heats up. We put this on for yesterday's afternoon adventure and it definitely helped keep her cool - she wasn't panting at all. Putting on the wet harness was a bit uncomfortable for her at first, but she got used to it. It fits really nicely too. She is a little over 50 pounds at 9.5 months and the medium fits well with room to grow. I know this will get dirty so I'm curious how well it will wash and retain its colour/look.