For accurate replica reproducing intra and extraoral tissues, impression materials are able to transform into a rubbery or rigid solid in the mouth within

To produce accurate replicas of intra and extra oral tissues, the impression materials should be: Sufficiently fluid to adapt to the oral tissues.  Viscous enough to be contained in a tray.  Able to transform (set) into a rubbery or rigid solid in the mouth in a reasonable time (less than 7 min).  Resistant to distortion or tearing when removed from the mouth.  Dimensionally stable long enough to allow one or more casts to be poured.   Biocompatible. Cost-effective in terms of time as well as the expense of the associated processing equipment. Phillips 12 ed page no 152