<prompt> Gypsum product having least expansion:Impression plasterModel plasterStone plasterDie stone  <response>: DENTAL STONE, HIGH STRENGTH TYPE IVThe principal requisites for a die material are strength, hardness, and minimal setting expansion. To obtain these properties, modified α-hemihydrate is used. The cube-shaped particles and the reduced surface area produce such properties without undue thickening of the mix. This material is also called die stone. 