Several mechanisms are involved in 2D fiber spinning. First, a take-up velocity is assigned at the end of the computational domain. This velocity leads to significant geometric changes and to the development of the free surface. A swelling may develop at the die exit, but it is usually not a critical feature; it is quickly hindered or annihilated by the take-up (pulling) velocity.

The take-up velocity plays a dominant role in the free jet. A transverse velocity gradient exists in the channel, while the free jet is endowed with an axial velocity gradient. The occurrence of a significant strain rate is typical for fiber spinning. Many melts involved in fiber spinning exhibit a more-or-less pronounced strain-hardening behavior, as this property is known to enhance the stability of the process.

A moderate take-up velocity is sometimes applied in continuous extrusion processes (for example, for guiding or stabilizing the extrudate). Here, the draw ratio is close to 1, which means that the elongation rate involved is often negligible; such cases should not be regarded as fiber spinning.

To some extent, 3D fiber spinning combines the effects encountered in 2D fiber spinning with some of those seen in 3D extrusion. That is, the flow has a strong elongational component due to the take-up velocity, as well as effects resulting from the velocity rearrangement in the 3D geometry. This take-up velocity leads to significant geometric changes. A swelling may develop at the die exit, but it is usually not a critical feature; it is quickly hindered or annihilated by the take-up (pulling) velocity.

The kinematics of 3D fiber spinning involves a transverse velocity gradient in the die, while the fiber itself is endowed with an axial velocity gradient. Consequently, the aspect ratio of some details in a cross-section of the fiber may differ significantly from the corresponding aspect ratio found at the die exit.