This document specifies a test method for determining the mechanical viscoelastic properties of interlayer materials. The interlayers under examination are those used in the production of laminated glass and/or laminated safety glass. The interlayer viscoelastic properties are needed in order to determine the load resistance of laminated glass. From the tensile modulus in particular conditions of temperature and load duration, an interlayer can be placed into a family that relates to a specific interlayer shear transfer coefficient. This value can be used in the simplified calculation method described in EN 16612. Informative Annex D explains the background to the determination of families relating to a specific interlayer shear transfer coefficient.