Flexible Filament Without the Guesswork

TPU and TPE are the families people mean by flexible filament. The Shore number tells you how soft the result is. A 95A TPU is firm, closer to a shoe heel, and it is the sensible first spool. Softer grades collapse in the extruder, string across the part, and stick to themselves on the spool. There is no prize for starting there.

Give the strand less chance to escape

Flexible filament buckles if the extruder pushes harder than the nozzle can melt, or if there is a gap between the drive gear and the hot zone. Direct drive shortens that gap. A Bowden tube can work with firmer TPU if the tube is tight and the speed is humble, and it will fight you as the spool gets softer. Print slowly. Use less retraction than you use for PLA, because a long retract pulls soft plastic into a place it can jam. Squash the first layer enough to stick, then do not baby the cooling. These parts often want less fan than you expect, or they refuse to bond between layers.

Dry the spool. Moisture shows up as pits, strings, and a rough surface that looks like a mechanical fault. Keep the spool in a sealed box with desiccant between prints. And design the part for flex: thin sections where it should bend, thick sections where it should hold a screw, and no sharp inside corner at the hinge.

• Disable a long coast or wipe until the basic cube is clean.
• Keep the path from gear to melt as constrained as the printer allows.
• Do not print flexible filament on a sheet you also use for food.
• Test a living hinge with the grain of the layers, then against it. Keep the winner.