I'm a size 10 and they were also roomy enough that I didn't need a size up. They can also be worn barefoot and machine washed (but not tumble dried). They are much cooler in terms of temperature than traditional running shoes because they are made of mesh (with reinforced toe and heel for protection) and the sole is perforated on the inside to allow air to circulate. I use them to go outside and inside the house. I have a bump and a large callus on the side of my little toe which makes it difficult to wear traditional shoes as they rub against the bump and callus. This is one of the most comfortable shoes I've ever worn, if not the most comfortable.