...or literally "Boiled Leather", was armor made from leather that hardened by exposing it to boiling water, hot wax or oil, then formed into the desired shape. The process chemically changes the leather fibers, plasticizing them so that as they cool after treatment, they become a more rigid material, almost like a shell.

The leather would be cut to the desired outline, heat treated, then formed into the desired shape. It might have been tacked to a wooden former or sometimes tied to the individual with strips of cloth to take the necessary shape. For a few minutes after it comes out of the water, oil or bees wax, it is very flexible and stretchy, so it is easy to mold to the desired shape. As it dries, it becomes stiffer and more rigid. The longer the leather is exposed to the heat source the more rigid it becomes, sometimes almost as stiff as wood.

There is a trade-off, though. The more rigid it becomes, the more brittle it gets. Like modern thin plastic that is normally flexible, when plastic get really cold, it can be easily snapped into separate pieces. Kind of like it being easier to break a wooden board with a blunt blow than it is to break a rope. When something can no longer bend, it may snap under stress.

Bee's wax also had some Pros and Cons. The material was readily available, imparted a pleasant aroma, and helped make the leather water resistant. Bees wax also has some natural germicidal qualities to it. The bad news is that wax hardened leather is actually EASIER to cut with sharp steel than untreated leather. This works something like freezing a roast before slicing it. Leather treated this way was useful for stopping blunt blows like from a fist or club or mace, but hardly slowed a sword or lance at all.