The Cold End
Discussions around the Ender 3’s extruder will generally point out the likelihood of the filament bending in the cold portion, after it passes the toothed gear. This is a bigger problem with flexible filament because… it bends, and the motion of the extruder motor won’t be transferred properly.
An upgraded all-metal extruder can help with the potential bending of the filament in the extruder, but if you’re on a smaller budget, this extruder upgrade from Thingiverse addresses the issue. Some users have even recommended using a straw to keep the filament straight – the key is to avoid bending of any kind.
On the topic of upgrades, be sure to check out our list of the best Ender 3 upgrades and mods.
The Hot End
As stated earlier, an upgraded all-metal hot end can make printing with TPU easier since it eliminates the PTFE tube that could cause issues with flexible filament. In addition, these types of hot ends can reach higher temperatures, which gives you access to a whole range of other materials.
The Bowden Tube
The Bowden tube can sometimes be at fault for allowing the filament to bend too much, causing a problem. The upgrade kit linked above has a fresh Bowden tube, but you can also opt for a higher quality tube, which should result in easier movement of the filament to the hot end.