I have a confession. This week a roll of TPU filament purchased from Rigid Ink in March 2018 was discovered lurking in a box and it was time to print some antenna holders for an FPV drone.
The trouble with filament that's been left in storage, however carefully, is that due to the hygroscopic nature of certain filaments they basically become waterlogged. TPU is particularly badly affected by this. The roll I had was still factory sealed with a dessicant packet inside the spool and yet it was clearly wet. There was a slight hissing as the filament extruded out of the nozzle and the final print quality was terrible.
The fix? 60 minutes in the oven at 170f (the lowest my oven would go). An unbelievably simple fix for a problem I was concerned meant that this roll of filament was destined for the trash.
The headline image for this post shows a print with wet filament on the right and dry on the left. They were printed at a slight orientation difference but you can clearly see the dry TPU produces much better layer adhesion and more consistent extrusion.