Medical systems and methods including balloons having nanotubes are disclosed. In some embodiments, a medical system includes an elongated shaft, and an expandable balloon carried by the shaft and including nanotubes. The medical system is capable of cooling the balloon to less than about 37° C. In some embodiments, a method includes providing a medical device having an elongated shaft, and an expandable balloon carried by the elongated shaft and including nanotubes; and cooling the balloon to less than about 37° C.