To calculate the stresses on the walls of silos, it is necessary to have a good estimate of the ratio of horizontal to vertical stress. This ratio however is not known precisely, especially in cases of static stress as found in a mammoth silo. In this paper the influence of the wall stiffness on the ratio of horizontal to vertical stresses in situations with limit strain is investigated. A new test method is developed, with which the ratio can directly be measured. A key feature of this method is the comparability with the practice. The method uses reinforced rubber membranes which have the same order of radial stiffness as mammoth silos. Another objective was to determine the extent to which the ratio of horizontal to vertical stresses with limit strain is dependent on the internal angle of friction, ¿i. Special attention was paid to Jaky's formula, which is often used to calculate the neutral stress ratio.