Macroindentation tests were performed by means of a flat cylindrical indenter on high-density polyethylene (HDPE) and polyamide 66 (PA66). Commercial sheets were acquired for both materials, and specimens were extracted for differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermal recovery tests. In this way, the fabrication effect was correctly identified in terms of degradation, orientation, and mechanical performance. Specimens were also prepared for tensile tests, which were performed for comparison with indentation experiments. Indentation tests were carried out on the external sheet surfaces at different indenter diameters (1 and 2 mm) and test rates (from 0.1 to 20 mm/min). A very high correlation was found between the tensile test and indentation results at the different test rates. In particular, the indentation stress at fixed depth was a linear function of the tensile yield stress, depending only on the indenter diameter and not on the material type. Moreover, a threshold value for the thickness for a correct comparison among samples having different dimensions is discussed.