Why TPU strings and how the slow speed stops it

TPU strings because the flexible filament bends and compresses in the extruder instead of pushing through the nozzle. General studio practice: the fix is to slow the speed so the drive gear feeds the filament steadily, and to keep the retraction near-zero so the filament does not buckle between the drive gear and the nozzle. A soft TPU that runs at 60mm/s like a draft stringy across the gaps, and a TPU that retracts at 4mm like PETG jams in the extruder.

The speed and retraction bands that stop the strings

The seller has not published a TPU speed or retraction profile, so the bands are general practice. The companion troubleshooting guide covers the jams and the under-extrusion when the filament buckles in the extruder. This table sets the expectation that the speed and the retraction are the two most important TPU controls.

The drying workflow before the first TPU print

TPU is hygroscopic, and a damp TPU always strings. General studio practice: the spool is dried at 55°C for 6–8 hours before the first print, because moisture turns into bubbles and stringing that the retraction tune cannot fix. The listing ships the spool vacuum-sealed with desiccant, and the ecosystem practice is to dry the spool before the first run.

The drying cycle order

1. Set the dryer to 55°C. General practice: 55°C for 6–8 hours on a spool that has been open for a few days.
2. Leave the spool in for the full cycle. A half-dried spool still strings, so the full cycle matters.
3. Test-extrude on a tile. A clean, quiet bead means the spool is dry; a bubbly, popping bead means another cycle.
4. Reseal the bag after the session. The bag with the desiccant is the short-term home; a dry box is the upgrade for a long bench.
5. Store in a cool, dry place away from direct sunlight. The listing's storage rule; the sealed bag keeps the bench humidity out.

General practice: a spool that has been open for weeks in a 50–60% RH room may need a second drying cycle. The seller has not published an official drying temperature, so the 55°C band is general practice. The companion troubleshooting guide covers the storage dry box and the rotation rule.

The temp tower and the nozzle temperature

Before the calibration cube, the nozzle temperature needs a small calibration on a test tile. General studio practice: run a temp tower from 220°C to 260°C in 5°C steps, and read the layers against a window light. A layer that reads smooth and quiet at 230°C is the nozzle band, and the upper layers that pop or bubble tell you the spool still needs drying. The listing's 220–260°C band is the envelope, and the TPU practice runs the lower-middle at 220–240°C.

General practice: a 230°C nozzle, 50°C bed, 30mm/s speed, 1mm retraction lays a smooth transparent TPU wall. The seller has not published a TPU temperature profile, so the bands are general practice. The companion troubleshooting guide covers the jams and the under-extrusion.

Calibration checklist before the first TPU print

Before you run a real TPU part on the Tronxy Clear TPU spool, run this checklist. Each item is a general-practice step that catches the most common first-print failures, and none of them is a listing spec — the seller has not published a TPU profile.

1. Dry the spool at 55°C for 6–8 hours. Moisture is the number one stringing cause.
2. Set the retraction to 1mm at 20–30mm/s. A near-zero retraction keeps the filament straight.
3. Set the speed to 30mm/s. A slow speed feeds the filament steadily.
4. Set the nozzle to 230°C and the bed to 50°C. The listing's bands; the starting point for the calibration cube.
5. Turn the part fan off. A fan chills the soft TPU and clouds the transparent surface.
6. Slice a one-wall calibration cube. 0.2mm layers, 30mm/s, 230°C nozzle, 50°C bed, 1mm retraction.
7. Print the cube and watch the gaps. Clean gaps mean the profile is ready; stringy gaps mean the spool needs another dry cycle.
8. Record the settings. Write the nozzle, bed, speed, retraction and drying cycle on the spool label; the next TPU print starts from a known good state.

Common beginner mistakes on transparent TPU

A few settings catch out most new TPU users. Each row pairs the mistake with the symptom and the fix, and the symptom is what you will see on the bench.

Starter projects on the Tronxy Clear TPU

After the calibration checklist, the right starter parts teach the stringing-free workflow without wasting plastic. General practice: start small and flexible, so each test exposes one setting.

General practice: a clean transparent TPU cube at 230°C, 50°C bed, 30mm/s, 1mm retraction, and a dried spool means the profile is ready for larger flexible parts. The seller has not published a TPU profile, so the settings on your spool label are the working record. The companion troubleshooting guide covers the jams, the under-extrusion, the bed adhesion and the storage rotation.

The temp tower and the nozzle temperature band

Before the calibration cube, the nozzle temperature needs a small calibration on a test tile. General studio practice: run a temp tower from 220°C to 260°C in 5°C steps, and read the layers against a window light. A layer that reads smooth and quiet at 230°C is the nozzle band, and the upper layers that pop or bubble tell you the spool still needs drying. The seller has not published a temp tower, so the 5°C steps are general practice.

The nozzle temperature range

The nozzle temperature is the second most important TPU control after the retraction, and the range is 220–240°C in general studio practice. The listing's 220–260°C band is the envelope, and the TPU practice runs the lower-middle at 220–240°C. A nozzle that runs too high melts the soft TPU and oozes, and a nozzle that runs too cold under-extrudes the wall. The companion troubleshooting guide covers the under-extrusion when the filament buckles in the extruder.

What the Tronxy clear TPU competes with on the bench

The listing describes the Tronxy Clear TPU as low-odor, low-warp, not brittle, flexible and rebound-capable, and it rates the spool at Shore 95A with a 46D reading. General studio practice compares the clear TPU part on the flexibility, the rebound and the bed-prep axes rather than the brand name, because the slow speed and the near-zero retraction matter more than the label. The roundup compares the Tronxy spool against the common clear TPU competitors on the market, and the color comparison guide covers the 95A versus 90A versus 85A differences.

The working takeaway is that a clean transparent TPU cube at 230°C, 50°C bed, 30mm/s, 1mm retraction, and a dried spool beats a stringy print at any brand. The seller has not published a material-grade comparison, so the brand choices are covered in the comparison guides rather than here. TPU's rebound and shock absorption are the reasons it suits phone cases, watch bands, shoe insoles and drone parts rather than display models.

What to do when the clear TPU cube strings on the second print

A first clear TPU cube that prints clean and a second that strings almost always means the spool has re-absorbed moisture between sessions. General studio practice: a spool that has been resealed in the vacuum bag overnight stays dry, and a spool left on the bench for a week in a 50–60% RH room re-absorbs enough moisture to show bubbles. The fix is to dry the spool again at 55°C for 6–8 hours, and to reseal the bag after each session. The companion troubleshooting guide covers the storage dry box and the rotation rule, and this paragraph sets the expectation that the second-print stringing is a moisture problem, not a profile problem.

Retraction and travel speed after the temperature lock

Once the temp tower locks the nozzle band and the bed prep holds the first layer, the next tune is the retraction and the travel speed. General studio practice keeps the retraction near-zero at 0.5–2mm for a direct drive, and raises the travel speed so the string snaps before it lands on the part. The listing's 30–60mm/s is the print speed, not the travel speed, so the travel tune is a separate setting. The companion troubleshooting guide covers the full retraction diagnostic table, and this paragraph sets the expectation that the travel tune comes after the temperature and the bed prep.

The bed prep that keeps the first layer bonded

A warm bed and a clean plate are not enough if the bed surface is greasy. General studio practice: a clean PEI or glass plate at 50°C holds the first layer, and a dirty plate lets the first layer lift. The listing says the spool prints on a heated bed, and the ecosystem practice is to wipe the plate with isopropyl before each print. The seller has not published a bed-prep sequence, so the steps are general practice. The companion troubleshooting guide covers the bed adhesion when the first layer still lifts after the prep.

Frequently Asked Questions