The method is used for investigating the behaviour of specified specimens under specified impact stresses, and for estimating the brittleness or toughness of plastics. The test may be carried out according product standard with notched or unnotched test specimens. The test specimen, supported as a horizontal beam, is broken by a single swing of a pendulum, with the line of impact midway between the supports and, in the case of notched specimens, directly opposite the notch. The impact strength is expressed as the impact energy absorbed in breaking a specimen, referred to the original cross-sectional area of the test specimen.