I've got in my universe some super-humans that are able to run/fly on super speed. They actually have virtually no strict speed limit. I put the reflex/maneuverability related questions aside for now. I also don't consider the dangerous effects of acceleration itself on the body fluids and various organs.
The only limit that I'm interested into currently is that on the atmosphere, they are factually limited by the overheating caused by the friction of air with their body. At some point their clothes will probably catch fire (or their skin will), like meteorites do when entering in low atmosphere.
I though they can use a special suit to face this problem. (However, any other interesting solution would be appreciated as well.)
Are you aware on any material that can be used to conceive that kind of suit, that reduce the heating / the friction with air? And if yes, do you have any bare estimation of the speed that can be tolerable for a human body wearing it?