Amoring is a natural phenomenon that appears when shear stress produced by the flow is less than the stress that the bigger grains of sediment can resist and bigger than the stress that the smaller particles can resist. This produces, in the bottom of the stream, an increment in the number of non-dragged thicker particles that form a layer known as armor, with small-size material prevailing in the sediment transport. Drag in the bottom of rivers is very influenced by the presence of this phenomenon, mainly due to the increment of the resistant stress and the median diameter of the particles. This is a sufficient motive to discard direct application of sediment drag methods. The main purpose of this article is a revision of the state of the art, then to present the results of experimental research that consist in the development in time of the phenomenon and its influence in the transport of sediment. Also, some modifications to the most widely diffused formulas are presented in order to improve their results.