So recently I'm working a speculative science fiction universe where I'm trying to adhere as close as possible to the laws of physics and the possibilities of technology. I want to have mecha (because they're cool) but the square-cubed law obviously makes such things very difficult to make since current materials need to be pretty heavy to provide tank level protection.

So I ask: Are there any materials, real, almost real, or could be real that could provide protection similar to tank armor at a fraction of the weight?

Note: The practicality of producing the substance is of no object. Just the possibility of its existence.

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    $\begingroup$ Carbon nanotubes are your best bet. $\endgroup$ Commented Jan 5, 2018 at 2:54
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    $\begingroup$ I don't think it would be possible to get what you want and adhere to physics, with any of the technology we have right now. For me, its mostly because the skeletal structure of your mecha would need to be incredibly sturdy to be useful and also needs to be able to absorb impacts from multiple directions. You would have much more fun focusing on your mechas than making them obey the laws of physics. $\endgroup$
    – Shadowzee
    Commented Jan 5, 2018 at 3:46
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    $\begingroup$ Armor is specialized for the type of attack it is defending against. Defending against a HE round is different than defending against a sabot round, which is again different from defense against a shaped charge round,and differnt again from a pure kinetic round (rail gun). In Iraq, the US military ended up welding simple steel cages onto vehicles to protect the armor against RPG's with shaped charges. $\endgroup$
    – pojo-guy
    Commented Jan 5, 2018 at 4:35
  • $\begingroup$ How does lighter armor make mecha more practical, especially when conventional alternatives (eg tanks) would benefit even more from lightweight armoring? The problem isn't square-cube law per se, it's surface area, and mecha are going to lose out to AFVs in that respect regardless of the armor technology available. $\endgroup$
    – Catgut
    Commented Jan 5, 2018 at 21:36
  • $\begingroup$ Well, because the robot has is going to be physically larger than the tank while in order to sport the same or similar firepower its going to be heavier and put a higher strain on motors, servos, etc. I'm well aware that a tank with the same firepower is going to be better in almost every respect to a giant robot. Its not the practicality that's the concern, its the ability to have robots serve a similar function to tanks while remaining, well, tanky. $\endgroup$ Commented Jan 6, 2018 at 0:52

5 Answers 5


A particularly interesting armor that exists currently is the "Dragon Skin" armor.


Basically this armor is made of small overlapping ceramic plates that are covered in in a textile, much like scales. As a result the armor is very good at stopping projectiles without adding too much weight. Now, instead of just ceramic plates and fabric, make it out of multiple graphene layers on top of titanium plates. This should make for some seriously tough armor that has a great strength to weight ratio. Maybe put an inner layer of some type of rubber, or if you want to be really fancy some kind of non Newtonian fluid that hardens on impact so that your armor can absorb some extra kinetic energy. Keep in mind, however, that generally better armor means the other guy just brings bigger guns and eventually the guns will win. So unless you can dodge, (very difficult), you need to either strike first, have some really fantastic point defenses, or both!


I propose you use reactive armor without the standard armor components.

The Wikipedia has some cool stuff. https://en.wikipedia.org/wiki/Reactive_armour

reactive armor
from https://media.defense.gov/2017/Mar/07/2001708258/400/400/0/170228-A-ZZ999-777.JPG

Standard reactive armor is explosives outside the normal shell. The soldiers here are putting the reactive armor components on their tank. Your armor would just be shaped explosives. When hit, they go off with the explosions knocking back whatever impacted the armor. Explosive chemicals are lighter than the equivalent volume of metal. You can make them lighter yet because this is science fiction. The Wikipedia calls this directed energy reactive armor

Another very cool idea and from the same Wikipedia page: electric reactive armor

Your armor is two thin conductive plates with a gap. An incoming penetrator closes the gap and the circuit. A capacitor then pours current into the incoming missile, and resistive heating turns it to plasma. I think my superconducting railgun projectile would go right on through that so good for you we are on the same team.

My own idea: deflective induction armor. Instead of armor there is a magnetic field. Incoming conductive projectiles develop eddy currents and consequently magnetic fields in opposition to the one on the armor. A field out far enough from the tank (possibly maintained with antennae) could produce a field which could deflect incoming projectiles so they did not hit. This sort of armor would work well against particle beams and also my superconducting railgun projectile.

  • $\begingroup$ If the Mechas are in battle, their defense based around an antennae, wouldn't the antennae be a massive weakness? Is the magnetic field needed safe for humans to be near? $\endgroup$ Commented Jan 5, 2018 at 12:26
  • $\begingroup$ @Lio Elbammalf - The antennas would be a weakness. If you were tramping through a forest you might break them off on trees. If you are in a desert and you can prevent enemies from getting close, and the antennas protect themselves from incoming rounds from a distance, that could work. Re humans: strong magnetic fields might have paramagnetic effects on water etc. Best to keep the field outside the mecha. Do not let your friends outside the mecha walk through the field. $\endgroup$
    – Willk
    Commented Jan 6, 2018 at 0:22

Boron Nitride (BN)

Some people mentioned carbon nanotubes, but for heavy duty armor, they might not have the best properties. In particular, they are susceptible to heat damage and can undergo adverse chemical reactions at high temps, such as decompostion in air.

Boron Nitride, on the other hand, is a viable option. Not quite as strong as carbon nanotubes, they can be formed into similar molecular structures. There are also diamond analogs of BN, which have a similar hardness.

Ceramic plating (such as silicon nitride ceramics) reinforced with BN nanotubes would have significantly increased strength and resistance to thermal shock.

  • $\begingroup$ Aggregated diamond nano rod would also work. If I'm not mistaken it is the hardest substance we have right now. $\endgroup$
    – Nick
    Commented Jan 5, 2018 at 18:06

This breaks the "like tank armor" rule, but...

Shoot the incoming projectiles

This is very, very hard to do, but you said not to worry about that ;)

When two projectiles collide at these kinds of speeds, they will tend to behave much more like liquids than solids. Imagine shooting an egg that was being thrown at you. The egg will still reach you, but it will be broken up and the pieces distributed over a large area. The same sort of thing would happen to an incoming slug, completely negating its effectiveness.

High explosive rounds would behave a little differently, and, depending on the type of explosive used, would maybe explode prematurely.

If the incoming round is made of something very hard like tungsten, it might shatter rather than (for lack of a better word) splat, but the effect will still be the same.

This is a real-world technology for larger, slower moving projectiles such as missiles. A quick google search found me this German armament that seems to attempt this for incoming artillery, mortars and missiles.

This might be easier if you can use a high-power laser to superheat the projectile as it flies towards you, but it would have to be a very powerful laser. The time the projectile spends in the air is very short, and convection will be working against you.

  • $\begingroup$ One real world version of this is called the trophy system, and it’s Israeli if I’m not mistaken. $\endgroup$
    – Nick
    Commented Jan 5, 2018 at 16:55

The shells of Crayfish, notably mantis shrimp claws can withstand a bullet, and they are relatively lightweight, and naturally occurring, you'd just need a safe way to farm them.

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    $\begingroup$ I'm not sure I believe that. Do you have any evidence for the strength of crayfish shells? Also, crayfish are decapod crustaceans (related to lobsters and crabs), while mantis shrimps are stomatopod crustaceans. They are in different orders, and not so closely related. $\endgroup$
    – kingledion
    Commented Jan 7, 2018 at 21:16
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    – Secespitus
    Commented Jan 8, 2018 at 9:20

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