So I have heard (in scuttlebut) that the mongols wore a silk shirt to protect them from arrows.

What evidence is there for this?

Carpini specifically mentions them. Some Byzantine medical manuals talk about their effectiveness but I can't remember whether they specifically mention them in a Mongol context. I wouldn't classify these shirts as armour. They don't stop weapons from causing injury.

I was referring to the story about being pierced by an arrow, but the silk not being torn so that the arrow could be pulled out without leaving behind any material in the wound.

I wonder if Carpini et alias were going on first-hand information or if they were merely repeating myths.

No way to tell if these shirts were hiding armor of some sort inside the layers of cloth. That would be one explanation for the stopping power of a cloth shirt.

As to the historical citing’s, I don’t know but it seems there were rumors circulating from China to the middle east on this, I don’t know them though. As to the role the silk shirt plays in acting as armor, I’ll elaborate as people somehow think the shirt was stopping the arrow or preventing the wound. If you look into how an arrow flies and how it kills it is helpful to understanding what role the silk shirt did in the ‘armor.’ There are a few articles from bow hunting that will explain what happens when you 'shoot' an arrow at a deer. If you want to be more graphic you can look for pictures of the wounds that occur (external and internal) and trail of blood from after the animal is hit with the arrow.

The silk does not stop the arrow it aids in your ability to pull the arrow out. An arrow rotates as it flies and when a broad head style arrow strikes flesh it doesn’t go straight in, it screws itself into the target and your flesh closes around the hole to protect itself. If you try to pull the arrow strait out you rip the flesh, causing even more damage and risk of killing the person hit, If you push it through you cause further injury to the other side, you essentially need to unscrew the arrow to get it out without much further damage. In Europe special tools were made to try and help get the arrow out after you had been hit. You can also just cut it out but that requires much more interesting surgery.

The silk would wrap itself around the arrow as it entered your body, this didn’t allow your flesh to ‘close the hole’ as the silk was still in the hole and it did allow for easier withdrawal of the arrow by ‘teasing’ the silk. It also didn’t prevent injury to the body or internal structure but it would keep the ‘after damage’ of an arrow hit from making things worse.

Thank you jonathon

Color me skeptical, but how does a broadhead arrow "screw" itself into a wound?

Typically the broadhead doesn't cause the twisting but the arrow as it flys will spin (Which at the very least is a function of using feathers as fletching) so when it hits it has some rotational inertia so that the arrow keeps turning after it hits the target.

Yeah I would be sceptical too but in the archery world, well more in some circles of the tradtional archery world, there is a debate over single versus double bevel broadheads and I'll spare you all the details but the proponants of the single bevel claim that it causes the arrow to twist more in the target then the double bevel. And they have some testing to back that up. So arrows twisting after impact has been studied and is a known thing.

I should add that I would think that war bows would cause more pass throughts than not. Both complete pass throughs or at least the broad head sticking out both sides. Most deer hunters try to get pass throughs when hunting with tradtional bows. But I would be interested in finding any proof of this happening. I have always heard this tossed around as fact.

Yes the broad head does not cause the twisting/spinning, it is the fletching, arrows spin in flight. Much like a rifled barrel will put a spin on the bullet to keep the flight strait and accurate, you do the same with arrows. There are old records talking about how much an arrow should spin in flight so it has been demonstrated this wasn’t a modern concept, also real feathers impart the spin naturally while when we use modern materials we just fletch the arrow at a curve. Due to the spin on the arrow it will continue to turn slightly as it enters the target. The concept of ‘screwing’ or perhaps twisting into the target is more accurate than thinking of the arrowhead as going straight in.

http://www.youtube.com/watch?v=I9q3zM65KSU
http://www.youtube.com/watch?v=aNI9BG87qcI&feature=related

I mentioned the broad head because it is the cutting arrow head, the bevels cut a wide arch as opposed to a bodkin which is relatively strait and thus doesn’t cut into the target, it acts more like a thrust.

As to pass through I don’t think anyone will argue that you want the arrow to go through as much as possible, I think it would be harder to do on a battlefield as most people on the battlefield will be wearing some type of armor and to get to the flesh you have to get through that armor, or hit an unarmored part. Much of the energy of the arrow will be lost when trying to get through the armor, as seen in all the threads on arrows going through armor. Once you get to the flesh the remaining energy will take the arrow into the body, which may or may not be enough for pass through, most likely not enough considering any decent armor. The silk shirt wasn’t there to keep you from dying from the initial hit of the arrow, if that killed you the shirt didn’t matter; it was to keep you from dying when the surgeon is trying to take the arrow out.

In the late 19th / early 20th century many bullet proof vests were made of layers of silk.
A doctor from Arizona, I can't remember his name, in the 1880s designed silk vests that provided protection from arrows. Eventually, he was producing silk vests that prevented bullet penetration.
Silk is a pretty tough material.