<prompt> The impression material with lowest viscosity isPlaster of parisAgar-agarZinc oxide eugenolElastomers  <response>: Impression plaster is a β-calcium sulfate hemihydrate used at a waterpowder ratio of approximately 0.5 to 0.6. Its fluidity makes it suitable for making impressions of soft tissues in the uncompressed state, a characteristic of mucostatic impression material.Ref: Phillips 12 ed page no 177 