Gypsum product having least expansion:
Impression plaster
Model plaster
Stone plaster
Die stone
DENTAL STONE, HIGH STRENGTH (TYPE IV)
The 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.