The type of chainmail I always knew about was the 4 in 1. Called that way because each ring is crossed by 4 others as seen in the following image.
But there are tighter weaves as well. For example the following image shows a 6 in 1 which has six rings passing through any one ring.
This clearly leads to stronger chainmail which is harder to pierce or slash through. So it got me thinking how does this get represented in games. Chainmail was a very common piece of armor. Its invention attributed to the celts it became the standard armor for the Roman Empire under the name of lorica hamata.
Unlike the more commercial examples shown above the real thing (lorica hamata) was made of punched and riveted rings as shown below. This made for a stronger chainmail. Half the pieces were solid rings of iron and half the other were riveted shut. So a weapon was not prone to easily separate them and bring the rings loose.
As you might imagine making the riveted part of the mail was very hard. The following video shows how to make riveted mail with today's comforts like electricity, power tools and nails. Just imagine doing this back in the middle ages. Chain mail was a cherished item, very costly and quite literally the difference between life and death on the battle field.
So shouldn't all that hard work pay off on the battle field? What about paying an extra for 6 in 1 or even 8 in 1 chain mail which adds more protection to the wearer? And how should this be represented in the game? As a +1? A +2? Where does this leave plate mail and full plate then? What mechanical benefits does it convey? Is armor encumbrance represented well enough in the game to be worth it?
D&D economics is to inflated to make a real difference. After all chain mail is cheap relatively speaking. Once a character gets going and survives the first few adventures there is little interest in worrying about chainmail anymore. In Pathfinder chainmail gives +6 armor bonus, costs 150gp and has a -5 armor check penalty coupled with a +2 max dex bonus. Full plate costs 1500gp has a +9 armor bonus, -1 max dex bonus and -6 armor check. Is there niche for chainmail costing between 150 and 1500 gp that can give +7 or +8 bonus while still have the same low penalties for chainmail? I sure think so. Thoughts?
Images from http://www.chainmailbasket.com/ , http://www.legionxxiv.org/loricapage/ & http://en.wikipedia.org/wiki/Lorica_hamata