TPU is a flexible filament that can produce amazing prints, but it also requires some special settings and adjustments to print well. One of the most important factors is the tension of the extruder, which affects how well the filament is fed into the hotend and how much pressure is applied to it.

The tension knob is a small screw or dial that controls how tight or loose the spring that presses the idler bearing against the filament is. If the tension is too high, the filament can get crushed or deformed by the idler, causing jams, underextrusion, or poor quality prints. If the tension is too low, the filament can slip or skip in the extruder, causing overextrusion, stringing, or blobs.

To adjust the tension knob properly for TPU, you need to find a balance between enough grip and enough flexibility. Here are some steps to follow:

1. Load the TPU filament into the extruder and preheat the hotend to the recommended temperature for your brand of TPU.
2. Start with a low tension setting, such as turning the knob counterclockwise until it stops or loosening the screw until it is barely touching the spring.
3. Print a test cube or a calibration pattern and observe how the filament behaves in the extruder. Look for signs of slipping, skipping, or grinding.
4. If you notice any of these problems, increase the tension slightly by turning the knob clockwise or tightening the screw a bit. Repeat step 3 until you find a setting that eliminates these issues.
5. Check the quality of your print and look for signs of overextrusion, underextrusion, stringing, or blobs. Adjust the tension accordingly until you get a smooth and consistent extrusion.
6. Remember that different brands and colors of TPU may require different tension settings, so you may need to tweak them for each spool you use.