Boiled leather

Boiled leather, sometimes called cuir bouilli, was historically a popular construction material for armour. It consists of thick leather, boiled in water (some sources hold that oil and wax were used as well, others posit the use of ammonia from fermented animal urine). The boiling causes the leather to become hard and brittle, gaining some resemblance to the properties of wood. Since the leather remains flexible and stretchable a short time after the boiling, forming it to the needs of the armourer is quite easy, making it a cheap, light and convenient alternative to bronze, steel, and other historical materials.

Cuir bouilli has also been employed to bind books.