The fiber spinning process presents a unique engineering challenge, primarily due to the effects of shape variations, heat and possibly the viscoelastic behavior of the materials typically used.

The difficulty in determining the proper die geometry and processing conditions, given the desired final fiber size and shape, further increases when those thermal and elastic effects are significant, which becomes more likely when high production rates are sought.

POLYFLOW predicts the fiber shape given the spinneret geometry, or combined with the die design capability, the correct spinneret geometry to produce a desired final fiber shape for axisymmetric and 3D fiber geometries. POLYFLOW also predicts the behavior of the fluid inside the die and within the drawn fiber once it is out of the die and provides information on the whole domain such as particle trajectories, temperatures, velocities, and tensions.

POLYFLOW is of particular help in designing spinnerets to generate fibers with complex cross-sections, such as hollow fibers.

In addition, since the fiber is pulled from the spinneret, the final dimensions of the fiber are difficult to determine. The effects of viscous heating and air cooling must be monitored to ensure that the material does not degrade because of extreme local temperatures, often difficult to measure because of the small size. The cooling process throughout the fiber often induces steep temperature gradients despite the tiny size of the fiber. Crystallization effects and phase change affect the material properties of the resin, hence the internal cooling rate. The stresses and deformation of the material must also be predicted to avoid the fiber from breaking. All these effects complicate the design of the fiber spinning process.

Special reduced-order models for fiber attenuation including surface tension and viscoelastic effects have also been developed in POLYFLOW.