I’ve been trying to print some things in TPU, using a fairly soft 85A TPU, and I keep having under extrusion.
I’ve already reduced speeds to max 25mm/s, and reduced retraction. My printer uses a direct drive extruder, and as far as I can tell, it’s grabbing the filament just fine. I’m printing at 240°C, using my default 0.4mm volcano CHT brass nozzle.
For me, completely disabling retraction helped out a ton. It went from a stringy mess to mostly clean prints. Other than that, slow speeds and finding the right temperature for my printer/filament got my prints pretty nice.