The mixing of non-Newtonian materials such as pastes, plastics, resins, and so on, involves factors distinctly different from those involved in the mixing of Newtonian fluids. A rotating propeller immersed in a pastelike material or a viscous liquid affects only a small portion of the total mass, leaving the greater part of it relatively undisturbed. Semisolids, viscous liquids, and heavy pastes require the mixing services of devices which are capable of affecting every portion of the material and achieving a homogeneous state by pushing one portion of the mass into another portion. Factors requiring special attention are the physical preparation of the materials, the behavior of the material under flow, and the effect of the order in which the ingredients are introduced into the mix. For highly viscous materials such as elastomers, equipment is often selected on the basis of its ability to shear material at low speed, or to wipe, smear, fold, stretch, or compress the mass being processed.