Buckram is a stiff cloth, made of cotton, and still occasionally linen, which is used to cover and protect books. Buckram can also be used to stiffen clothes. Modern buckrams have been stiffened by soaking in a substance, usually now pyroxylin, to fill the gaps between the fibres.
In the Middle Ages, "bokeram" was fine cotton cloth, not stiff. The etymology of the term is uncertain; the commonly mentioned derivation from Bokhara is, according to the Oxford English Dictionary, uncertain.
Millinery buckram is different from bookbinding buckram. It is impregnated with a starch, which allows it to be softened in water, pulled over a hat block, and left to dry into a hard shape. White buckram is most commonly used in hatmaking, though black is available as well. Millinery buckram comes in three weights: baby buckram (often used for children's and dolls' hats), single-ply buckram, and double buckram (also known as "theatrical crown").