plaster of par·is -'par-əs n a white powdery slightly hydrated calcium sulfate CaSO4·1/2H2O or 2CaSO4·H2O that is made by calcining gypsum, forms a quick-setting paste with water, and is used in medicine chiefly in casts and for surgical bandages
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calcium sulfate hemihydrate reduced to a fine powder; the addition of water produces a porous mass that hardens rapidly. It has been used extensively in making casts and bandages to support or immobilize body parts, and in dentistry for making study models.Medical dictionary. 2011.