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In this world human-like people have skin that is unbelievably difficult to cut through and I was wondering what biologically creatable material is flexible enough to act as skin but it also essentially impossible to penetrate with a medieval era spear.

Same size as humans with a 30% threshold if you need it.

Same size planet as earth with similar atmosphere and minerals, again minor changes necessary are ok e.g. 10% more aluminium or something.

It can be any material that could theoretically be made by a body e.g. some theoretical polymer.

Must be based upon a real material that is either believed to exist by reputable sources or does exist. Minumum handwavium, please.

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    $\begingroup$ So your requirements are, 1) it must be possible for a biological organism to synthesize it and 2) it must be able to stop a medieval spear from puncturing the creature and 3) It should be as flexible as human skin? $\endgroup$ – James Aug 3 '18 at 16:18
  • $\begingroup$ @James yes, yes, not necessarily, at least almost as flexible $\endgroup$ – P.Lord Aug 3 '18 at 16:25
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    $\begingroup$ dailymail.co.uk/sciencetech/article-2094364/… Technically the skin is grown around the goat-spider-silk stuff though. All I had to search for was "bullet proof skin". $\endgroup$ – Aify Aug 3 '18 at 16:59
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    $\begingroup$ I would be careful about your use of the word "cut" with spears. Spears weren't designed to cut, they were designed to pierce. Something that could withstand a slash from a sword likely wouldn't be immune to that type of piercing damage. $\endgroup$ – Sarah Stark Aug 3 '18 at 20:39
  • $\begingroup$ I second @SarahStark's comment. The difference between cutting and piercing is quite substantial. Many structures that are impervious to cutting are easily pierced. $\endgroup$ – Cort Ammon Aug 4 '18 at 6:30
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Meet my newest skin upgrade, with an advanced apology for the crudely-rendered schematics.

Cutaneum

enter image description here

As you can see, the image looks just like the average cross section of the integumentary system, except with a few modifications.

  • Special Hair is just like ordinary skin hair, except that its actually spidersilk with carbon nanotube enhancement. You get to be a little bit like spiderman, except you don't shoot webs from your palms only - you naturally grow controllable super-spiderslik from every special follicle of your skin. Each strand of special hair is not at all extraordinary on its own, but combine it with the modified sweat secreted from special follicles and each strand of special hair will interleave into an impenetrable full-body mesh.
  • Special Follicle is your new limb. With one of this, you can grow a single special hair, vary its length, drench it in gluey-cementing sweat, or drain such sweat from such hair. What's more is that you can choose to semi-consciously control the flexibility and hardness of the resulting hairy-silk armor to better suit your needs.
  • Non-Newtonian Fluid Reserves (NNFR) are cells containing non-newtonian fluid. Instead of a layer of fat, or of porous composites, or of rigid armor, I give you a single layer of impact-responsive units. Each NNFR unit is coordinating with all the others to allow your skin to flow like liquid when you want to move, but harden like concrete when you get hit by strong forces. This way, all the kinetic energy of piercing weapons hurled at you will completely be absorbed and dissipated by these cells. That is, if said piercing weapons get past your already-impenetrable carbon nanotube-infused spider-silk fur.

Summary of procedures for biological superskin

  1. Dot your skin with carbon nanotube-infused spidersilk-spinning follicles to resist deformation.
  2. Place a layer of non-newtonian fluid under your skin to absorb impacts.
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  • $\begingroup$ Spidersilk hairs are smart, but the non newtonian fluid is a terrible idea. Just imagine an airbag in a car that hardens the moment your face impacts with it. That is quite literally what you have on your skin. It might work to prevent things penetrating too deeply into your skin but as force absorbtion it'll kill you faster during impacts. $\endgroup$ – Demigan Aug 29 at 8:30
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Did you read about osteoderms? Dinosaurs and nowadays crocodiles have bone plates included in their skin which makes the skin really really difficult to cut.

crocodile skin

I dissected a crocodile and it is really hard to get through (best is to use a bone saw or an XL version of poultry scissors). These osteroderms are quite big on the back and smaller around the joints, which allows a full range of motion for the crocodile (even full gallop and high jumps).

Advantage: creates (together with a sturdy leather skin) some "walking tank" look, bone material can be easily synthetisized by the body

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    $\begingroup$ "osteoderms"... Latin is so useful for making the mundane sound too complex for mortals to understand. $\endgroup$ – RonJohn Aug 3 '18 at 21:55
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    $\begingroup$ Then call it skin ossifications ;-) damn... Even more Latin $\endgroup$ – JulPal Aug 3 '18 at 22:17
  • $\begingroup$ What about sweating? That's an integral part of human skin, and without it we're surprisingly limited. $\endgroup$ – RonJohn Aug 4 '18 at 15:10
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    $\begingroup$ @RonJohn That may be, but it wasn't part of OPs requirement about the skin $\endgroup$ – Sentry Aug 4 '18 at 23:28
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    $\begingroup$ @Sentry well, OP did say human-like. $\endgroup$ – RonJohn Aug 5 '18 at 1:34
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Spidersilk. Its biologically createable and properly woven through the skin it can protect against sharp objects. With enough fat tissue below it the blunt force impact can also be stopped.

The biggest problem would be bulk creation. As noted in this page: https://en.m.wikipedia.org/wiki/Spider_silk the creation of 3,4 by 1,2m took 1 million spiders and 4 years. On the other hand your glands could produce continuously rather than be destroyed during silk extraction and would grow with your body over the years so it should be feasible.

Edit: the spidersilk piece of cloth is ofcourse a solid slab of spidersilk, a skin wouldnt be a solid slab but would ideally be made of normal skin cells which pull the spidersilk on between them to create a network of cells and silk. This would be a feasible amount of silk assuming the creatures need to grow to adulthood giving it time to create enough silk as its body size increases. Thick groupings of spidersilk could be grown for protection against small-arms (if available) or environmental hazards like sharp thorn bushes and your neighbour stabbing you with a knife or arrow.

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  • $\begingroup$ On the topic of super-materials, do you have any idea of a way to make fat resist blunt force trauma better? Just thinking because I don't want to have to make them too fat. $\endgroup$ – P.Lord Aug 4 '18 at 17:44
  • $\begingroup$ I have asked a similar question already: worldbuilding.stackexchange.com/questions/107635/…. I see two options for improved fat: Make it heavier (difference between a 600kg car hitting you at 60km/h or a 6 ton truck at 10km/h, not exact numbera but you get the idea) or build the fat and body to spread the forces across as few organs as possible. Does not work well in case of carcrashes or falls as the body as a whole needs to decelerate then. $\endgroup$ – Demigan Aug 4 '18 at 19:21
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If you're willing to accept scales (probably a practical necessity for your question), I would suggest using keratin as the dominant material. You'd end up with a distinctive resemblance to pangolins, which for bonus points are a very real demonstration that what you're looking for is possible in nature. These are real mammals (albeit seriously endangered: due to its scales and meat being considered desirable, it is a huge target for poaching) with durable scales.

As for the keratin used for those scales, it's absolutely believable for humanoids to be producing it, if not necessarily observed in such quantity: it's the same stuff that your fingernails are made of, so human-like creatures with such an adaptation aren't likely to break suspension of disbelief (although there are side effects of having scales for skin, like the problem of keeping oneself clean, but that's probably out of scope for this question). I don't have hard numbers, but I believe they'd resist sword cuts just fine. A spear stabbing at them (not cutting, since what is essentially a long pointy stick is useless for slashing) would probably be blocked as well, although I'm not 100% certain on that.

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Different take - not skin, but fur

Imagine really thick, matted and layered hair - perhaps similar in properties to spider silk, or keratin.

Unlike plates that press into the underlying skin, impact resistance is high, and its tangled structure will slow and snag projectiles - similar to kendo armour or quilting in in a gambeson.

As a bonus, you get added warmth, flexiblility and it behaves like chain mail in spreading impact forces.

Your characters will look like imposing shaggy dogs, and probably smell like one too.

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Aramid fiber, aka Kevlar

Aramid fiber is an organic material, made of carbon, nitrogen, hydrogen, and oxygen. While evolving the mechanism to produce it may seem difficult, it's only a little more complex than the proteins found in silk. Of course aramid is significantly stronger than silk, as well as being impact and abrasion resistant. A person containing fiberous aramid in there skin would maintain skin flexibility (when you by aramid it comes in sheets of fabric), and the skin would be extremely resistant to tearing. As to being cut with a medieval spear, most places that sell aramid fiber also sell special serrated shears made of hardened steel, cut it would be a slow process requiring the best materials available at the time, possibly with a sharpening break required at some point.

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The movie Hitman centered around a plot of killing someone with sub-dermal armor. The YouTube Chanel Film Theory did a video explaining how this would be possible. Check it out: https://www.youtube.com/watch?v=PsE10pSYBos

For those without the time or desire to watch a 13 minute video, the answer is graphene. It can be made in sheets as thin as 1 molecule and it is made purely from carbon atoms, which also makes up a lot of the human body. When arranged correctly, carbon atoms form diamonds. So basically you have diamond armor just under your skin. You look normal, you weigh the same as a normal human, and your skin can stop bullets. A sufficiently think layer of graphene would only me 100 nanometers thick. It is supposedly 10 times better than steal armor. Plenty to stop a spear.

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  • $\begingroup$ Graphene has way different properties than Diamond, and its also extremely light compared to diamond. Does the video explain if the body could create and sustain it btw? For my supersoldier questions I would really like to know but I cant watch the video atm. $\endgroup$ – Demigan Aug 5 '18 at 22:16
  • $\begingroup$ The video was focused more on the plot of Hitman and doesn't necessarily fit exactly what you are trying to do. But I don't think it would be to difficult for a species of essentially humans to have the added feature a 100 nanometer thick layer of graphene under their epidermis. $\endgroup$ – Ian Johnson Aug 5 '18 at 22:52
  • $\begingroup$ What I'm worried about is creating it properly and how to keep yourself alive. We don't see creatures suddenly creating diamonds for protection because the requisites for creating it are tough. Graphene is easy to create in teeny tiny amounts, but not in large single quantities. The edges of Graphene also are very sharp, so much so that breathing a cloud of Graphene particles is hazardous. So how do you make sure you produce enough Graphene to be effective, and how do you deal with the fact that a pure sheet of Graphene stops even helium from entering your body? $\endgroup$ – Demigan Aug 6 '18 at 9:05
  • $\begingroup$ They would no be creating diamonds. I only mentioned diamonds as an example for carbon-based structures that are very strong. The people would have some biological system for creating what would essentially be an extra layer of skin that happens to be made out of carefully arranged carbon-atoms that happen to be the same arrangement as graphene. $\endgroup$ – Ian Johnson Aug 8 '18 at 19:12
  • $\begingroup$ I only mentioned diamonds as they are a carbon-based element but the requirements to creating it are practically impossible for a biological system to maintain. Graphene is also carbon, but creating it in useable quantities is unlikely to happen in a living creature, unless you know something I dont know. I would love to know if it was possible though. $\endgroup$ – Demigan Aug 8 '18 at 21:14

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