I bought these for a marathon where the temperature was 30 at the start and 43 at the finish and I was very comfortable the whole time with light running pants. The fit isn't tight or too loose, it's just comfortable and looks good, but it's also very functional. I would wear this for any run in the 30-50 degree range and use the zip for ventilation. It is NOT lined with microfleece, which is generally better for temperatures below 30C. We recommend. 5 feet 10 inches 155 pounds wearing medium