Amalgam exhibits a Poisson’s ratio of

Most rigid materials, such as enamel, dentin, amalgam, and dental composite, exhibit a Poisson’s ratio of about 0.3. Brittle substances such as hard gold alloys and dental amalgam show little  permanent reduction in cross section during a tensile test. More ductile materials such as soft gold alloys, which are high in gold content, show a higher degree of reduction in cross-sectional area and higher Poisson’s ratios.  Rubber has a Poisson’s ratio of nearly 0.5.  Cork exhibits little lateral expansion under compression and has a Poisson’s ratio close to 0.  This property has made cork a common material for sealing wine bottles. Ref:Craig’s Restorative Dentistry ed 14th pg 36