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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?

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    $\begingroup$ You are making a category error, by trying to relate something in the real world to super-powers. Just invent some material for the job, created by the same cause as the super-people. Trying to use realistic ideas in conjunction with super-powers just makes the powers look silly. $\endgroup$ – John Dallman Jun 3 '17 at 13:11
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    $\begingroup$ @JohnDallman Thank you for your input. However, the universe I'm building is contemporary by nature, and this super-speed is one of the very few fantastic elements. I don't think that introducing a paranormal element is an excuse to throw all realistic concerns and only use "super-"something to face any problem. $\endgroup$ – Cobaltway Jun 3 '17 at 13:21
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    $\begingroup$ I believe air compression may be a bigger problem than air friction at high speed. It certainly is in rocket landings. $\endgroup$ – Bellerophon Jun 3 '17 at 13:50
  • $\begingroup$ Yes, there is such a material. It is not a single material though. It is a series of layers put on spacecraft so that they can be protected from the heat generated by air friction when entering Earth at high speeds. It is referred to as 'heat shield' of the spacecraft. There are several different kinds of it. A simple google search can provide you the details. $\endgroup$ – Harmohit Singh Jun 3 '17 at 14:49
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    $\begingroup$ The friction is more or less negligible. The heat comes from compressing the air in front of the vehicle -- see Gay-Lussac's pressure-temperature law; it's the same effect which makes a bicycle pump hot when pumping air. At Concorde's top speed of Mach 2.2 the nose reached 153° C; spacecraft returning from orbit use ablative heat shields. $\endgroup$ – AlexP Jun 3 '17 at 15:23
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Another answer has suggested heat shield material, but that stuff is not flexible, and so is not suitable for clothing.

So, I'd suggest fabric made of woven metal threads, with a refractory metal chosen. This metal should have both a high melting point and resistance to oxidation. The obvious metal would be titanium, since this is already used in high-speed aircraft. Platinum might do, with a melting point about 100 C higher than titanium, with the lower strength acceptable since the cloth is not structural.

There are, of course, metals with much higher melting points, such as osmium, rhenium, ruthenium, tantalum and tungsten, but these tend to be much harder and less flexible. There is also an issue with oxidation rates - tungsten, for instance, oxidizes readily at higher temperature.

As to speeds available, I'd estimate something on the order of Mach 2 or (maybe, sort of) Mach 3. A limiting factor is that, unlike aircraft, people have to operate at speed at very low altitudes. The sort of aircraft which go fast enough to use titanium tend to do so at high altitudes where the air density is low.

Plus, of course, metal fabric just looks super-heroey.

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If you don’t want to stipulate super-material to go with the super-power, try the real-world supermaterials Worldbuilding post.

Note that the heating, as with a meteor, is due to ram pressure not friction.

Look or a suit made of superconductor. These are super for heat transfer as well as current, as loose electrons act as a fluid that transports heat—both the conductivity and thermal properties of metal stem from the same underlying source.

Meanwhile, have a heat sink on the back. It might look like a hedgehog! That would be cool, right?

So, the heating caused by the compressed air beats down on the front of the suit, and rather than building up to cause problems is immediatly dissipated off the cool back of the suit.

Besides actual superconductors, note materials with unusually high heat conductivity: Diamond, for example. Carbon nonotubes are popular for miracle materials. Although a different atomic structure than diamond, they can also have extreme properties that can be tuned by the angle at which they're rolled in addition to dopings.

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