TPU (thermoplastic polyurethane) filament is the most popular flexible material for 3D printing because of its great versatility. It's high durability and flexibility make it ideal for prototyping and even final products.

Advantages

  1. High impact resistance: very useful to manufacture protections for different devices such as mobile phones or tablets.
  2. High resistance to wear and tear.
  3. Abrasion resistant.
  4. Good cut resistance.
  5. Excellent chemical resistance.
  6. Cold bed printing. No need to heat the printing surface to generate adhesion.

Disadvantages

  1. Low temperature resistance: Despite having a wide working range, TPU softens above 50°C.
  2. Very low shore hardness makes it difficult to print with FDM
  3. Need to have a flexible compatible extruder. As it is a flexible material it is necessary that there are no gaps or holes through which the filament can escape.
  4. Low printing speed.
  5. Very hygroscopic. It is recommended to store the filament in a dry place when not in use.

Main printing parameters

Extrusion temperature

The correct temperature for extruding this material depends largely on your extrusion system. The range is 195°C to 240°C. The lower the temperature required to extrude the material, the better, as it will expand less (have less diameter increase). You will determine the correct parameter values for your 3D printer by performing a temperature test on this material.

Printing surface

The material has excellent adhesion, so it does not require a hot bed to stay attached to the base material. Even so, if you desire, you can operate at temperatures as low as 50°C. If you're printing on a smooth PEI surface, you must apply an adhesive (glue stick or lacquer) to create a barrier between the PEI and the component, or else it will be extremely difficult to remove the component from the surface.

Layer fan

When a part has a lot of detail, it is critical to help the plastic properly solidify so that it adheres properly. It is not advised to turn on this fan in the initial layers to enhance the part's adhesion to the surface.

Printing speed

Because it is such a flexible material, the printing speed will be slow so that the material can flow smoothly through the hotend. Average speeds of around 15-20mm/s for normal prints and 5-10mm/s for more precise prints are recommended, but these values are just guidelines. We advise keeping the speed below 35mm/s to ensure proper material extrusion. Each machine has a speed limit, which is best determined through experimentation and then reduced slightly to ensure proper printing with TPU and to prevent jams.

Layer height

The optimum layer height is usually 50% of the nozzle outlet diameter, but it can be lowered to 25% or raised to 75-80%. For a 0.4mm nozzle, an optimum layer height would be 0.2mm within a range of 0.1mm and 0.3mm.

Flow

It is critical to monitor the filament's tolerance to ensure it doesn't excessively stretch or compress as it moves through the printer. To be sure of the proper values, a test must be performed for every material used in the printer. With this material, it is common for the values to be over 100% to counterbalance the deformation caused by the extruder's thrust zone. The steps per millimetre must be precisely calibrated on the extruder to obtain this parameter correctly.

Retraction

The retraction value should be determined by testing using the hotend and extruder setup, to guarantee the best results. At first, you should print without retraction if you're using a flexible material since it doesn't handle shrinkage very well. However, you can use this variable when printing with TPU to improve your results if you have calibrated the other variables; the following estimates may be of help:

  1. Direct drive: 0.4mm & 30 mm/s
  2. Bowden: 2mm & 20 mm/s

Avoid clogging with TPU

Reduce the friction of the filament

Using such a flexible material, it is crucial to decrease as much as possible the friction between the filament and any part of the extrusion equipment to prevent jamming. The extrusion produces excessive friction, which deforms the filament, resulting in decreased flow and even clogging of the hotend. To minimise friction in the extruder, the spring tension must be set to the minimum possible without losing thrust, thus decreasing friction in that area. Capricorn tubes are recommended for Bowden extrusion setups as they are made from a low-friction material. 

Retractions

If the retraction length is poorly defined and very long retractions are made, the molten material will stick to the barrel walls in the cold zone of the hotend, resulting in a jam. To prevent this, retraction testing should be performed as described above. We suggest not activating the retraction function until you have a good understanding of printing with TPU.

Nozzle

A smaller nozzle at the outlet would increase the pressure required and make the material flow more difficult. A larger nozzle would reduce the filament pressure, reducing the friction in the entire system. We recommend a 0.4mm nozzle for printing with TPU. A smaller nozzle would increase the pressure at the outlet, making material flow more difficult.

Extrusion system

TPU can be extruded with any extrusion system, either bowden or direct extrusion, although direct extrusion is easier to get the best results. With either technique, the extruder must have the following characteristics:

  1. The thrust zone and the hotend must be as close as possible, and there must be no gap through which the filament can escape. Most contemporary extruders have solved this issue, but if yours is older, there are printed adapters for the most common extruders.
  2. The steps per millimetre must be correctly calibrated.
  3. The guiding tube must be as short as possible to reduce friction.
  4. All metal hotends require excellent cooling to prevent the material from adhering to the barrel walls, so if we plan to print only TPU and PLA we suggest using hotends with teflon tubes extending to the nozzle to prevent these issues.

Cleaning

The material may not flow properly if any particle clogs the hotend, so we recommend cleaning it with the 'cold pull' method or using cleaning filament.

Storing the filament

The material is extremely sensitive to humidity (hygroscopic). It must be stored in a dry place when it is not being used. Vacuum-packing the spool with an extra desiccant bag is advisable when you receive it at home. Since it is a costly procedure, we include an airtight bag with every spool in which you may store the filament together with its desiccant bag when not in use. Although, we advise using a filament dryer to dry the TPU Filament before printing.

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