Abstract The subject of the long-term reinforcement of soils with woven geotextiles and polymer grids is considered in this paper, with particular reference to the measurement of reinforcement stiffness and strength data for design. The robust nature of earthworks construction is likely to make material damage a more significant factor for soil reinforcement than for other applications of polymer materials. A clear distinction between the ideal behaviour relevant to the factory-produced material, and the expected changes from the ideal behaviour due to environmental factors and damage is recommended. A separation of the required reinforcement forces which depend on soil mechanics aspects and the available reinforcement forces which depend on reinforcement properties is recommended for calculation purposes. The aim is to clarify the selection of appropriate material properties and safety factors for design.