The rigid impression materials described till now are best suited for recording edentulous areas. Teeth or severe undercuts if present, would make the removal of such impressions difficult. The impression could distort or fracture on removal.The ideal impression material for accurately reproducing tooth form and relationship would be an elastic substance which can be withdrawn from the undercut area and return to its original form without any distortion.By definition, an elastic impression material is one that can transform from a semisolid, nonelastic state to a highly elastic solid state.