US Patent 7799841 Polypropylene foam

The present technology relates to a foam comprising a polypropylene material. The polypropylene material is produced in the presence of a metallocene catalyst, and the foam and/or the polypropylene has a branching index g′ of less than 1.00 and a strain hardening index (SHI@1 s−1) of at least 0.30 measured by a deformation rate dε/dt of 1.00 s−1 at a temperature of 180° C., where the strain hardening index (SHI) is defined as the slope of the logarithm to the basis 10 of the tensile stress growth function (log(ηE+)) as a function of the logarithm to the basis 10 of the Hencky strain (log(ε)) in the range of Hencky strains between 1 and 3.