Present-day rheological theory for the flow of dilute, concentrated, and highly concentrated filled polymeric solutions and its experimental basis are considered. The optimum type of fiber-forming polymer and solvent for preparation of spinning compositions is chosen. The advantages and disadvantages of various grades of activated carbon for the formation of filled fibrous sorption-active materials are noted. It was found that the nature of the activated carbon (the method of preparation, type of feedstock, porous structure, etc.) has a significant effect on the stability of the suspensions. The principal factors that determine the rheological characteristics of spinning compositions, such as the viscosity of the dispersion medium, the nature of the fillers, and the volume fraction and dispersibility of the solid phase, were studied. Their optimum values and their quantitative contribution to the change of viscosity were also established.