Izod impact testing is a standard ASTM method of determining the impact resistance of materials. A pivoting arm is raised to a specific height (constant potential energy) and then released. The arm swings down, hitting a notched sample and breaking the specimen. The energy absorbed by the sample is calculated from the height the arm swings to after hitting the sample. A notched sample is generally used to determine the impact energy and notch sensitivity. The unit of impact resistance gives you the energy loss per unit of thickness using the notches on your material.