Flow initiation indicates the yield stress at which a viscous ink will begin to flow. To achieve the desired 3D printed geometry with precision, an ink should retain its shape after being printed, thus behaving somewhat like a solid rather than a fluid. As increased shear stress is applied (when being printed), the ink will reach a yield stress at which it will flow more freely. Low viscosity inks that have no yield stress will flow without stress and are not ideal candidates for extrusion printing.