The skin and blubber of marine mammals provides protection from the surrounding environment, whether that be temperature, microbes, or direct mechanical impacts. To understand the ability of harbor seals’ (Phoca vitulina) skin and blubber to resist blunt force trauma, we tested the material properties of these tissues. We quantiﬁed two mechanical properties of the tissue: tensile strength and tensile stiﬀness, at two test speeds, three sample orientations, and two age groups. We found signiﬁcant diﬀerences in material properties between test speeds, orientation, and age of the animal, but did not ﬁnd a large diﬀerence with orientation. From this analysis, we conclude that harbor seal skin and blubber should be modeled as an isotropic non-linear elastic material with strain rate dependence. Moreover, we were interested in the eﬀects of freezing on the biomechanical properties. The material was tested fresh and after being frozen for four months. Frozen data revealed an increase in stiﬀness and strength for the skin (epidermis and dermis), but did not show a conclusive trend in the blubber material properties. While the availability of frozen marine mammal tissue is greater than that of fresh material, frozen tissue of harbor seals, especially the skin, cannot serve as an accurate replacement for testing of fresh material.