Polarized Light Microscopy and Materials Characterization The engineering material polycarbonate is unique for being both transparent and extremely tough at a reasonable price. This toughness has been attributed to subcrystalline structure that is small enough not to interfere with light transmission, yet significant enough to provide an additional resistance to deformation that is not available to typical glassy polymers. The study of both crystalline and near crystalline structures was undertaken with the aid of polarized light microscopy, differential scanning calorimetry, tensile testing, and fracture toughness testing. These studies have shown an increase in fracture toughness that is attributed to the growth of sub-crystalline structure. In addition, through the use of considerably refined preparation techniques, valid fracture toughness testing has been demonstrated with much smaller specimens than were previously considered acceptable. This will ease the study of newly developed materials, where availability of a large quantity of material is frequently an issue.