The flowing of the granular materials in bins is governed, particularly in the case of small ratios of aperture diameter to particle size, by the constant formation and breaking down of arches, known as dynamical arches. In unfavorable circumstances the arches may become stable and the aperture clogged. By building up a mechanical model of the arch the fields have been found in which a stable and a dynamical arch, respectively, may be formed, enabling a bin to be judged with respect to the danger of stable arch formation. A stable field allows of studying the interaction of arch stresses and deformation of materials starting from the stress curve of the arch as a function of the curvature, and from the curve of deformation of the material as a function of the stress. It is, therefore, possible that the elasticity of the material diminishes the stable field or even reduces it to zero. In the case of nonelastic materials, the collapse of the arch may be introduced by making the lower part of the aperture wall elastic. Stable arches can now be prevented from forming by choosing the elasticity of the resilient aperture wall in such a way that if the stress increases the wall expands sufficiently to cause the required collapse. The theory underlying this solution enables the elasticity constant and the required expansion to be calculated.