ASTM D3354
Standard Test Method for Blocking Load of Plastic Film by the Parallel Plate Method
5.1 Blocking develops in film processing and storage when layers of smooth film are in intimate contact with nearly complete exclusion of air. Temperature, or pressure, or both, can induce or change the degree of adhesion of the surfaces.
5.2 The procedure of this test method closely simulates the operation of separating film in some end-use applications.