Injection molding gets the attention, but walk through where TPU actually ends up — pneumatic tubing, cable jackets, hydraulic hose liners, sealing profiles, stretch films — and a striking share of it came off an extruder. Extrusion stresses the material differently than molding: the melt spends longer under shear, leaves the die with nothing to hold its shape, and has to be cooled and calibrated while soft. Each of those steps has a TPU-specific answer.
This is the extrusion deep dive, parallel to the single-topic piece on drying. For the all-process overview, see the TPU processing guide.
Editorial note: This is an independent educational guide. The parameter ranges here are illustrative of published TPU extrusion guidance, not a specification. Confirm screw, temperature, and die details against the current datasheet for the grade you run.
Why TPU extrusion is its own discipline
Three material facts shape everything downstream:
- TPU is shear-sensitive. Excessive screw speed degrades the polymer and the product — so the machine has to make output with geometry, not RPM.
- The fresh extrudate has low melt strength. It leaves the die soft and prone to distortion, so cooling and support carry more of the job than with stiffer melts.
- It is hygroscopic. The same <0.02% moisture rule as molding applies, and in extrusion the symptoms are unmistakable: throughput swings and die drooling.
Get those three under control and TPU extrudes well. Ignore any one of them and the line will tell you about it, usually within the hour.
Screw and barrel: built for a shear-sensitive melt
The published recommendation is specific: a single-screw extruder with a three-zone screw, L/D ratio of 25 to 30, and a compression ratio between 1:2 and 1:3 — preferably about 1:2.5 — with a continuous constant pitch of 1 D and radial screw-to-barrel clearance of 0.1–0.2 mm. Barrier screws can also work (undercut ≥ 1.2 mm). What is explicitly not suitable: short screws with a high compression ratio, which is exactly the geometry that brutalizes a shear-sensitive melt.
A few refinements have a proven record. Grooved feed zones improve feeding consistency, pressure build-up, and output — but they need cooling. Mixing sections help melt homogeneity as long as they are designed not to shear-degrade the material. And a breaker plate with screen packs is recommended; a combination of two 400 mesh/cm² backing screens with two fine 900 mesh/cm² screens has given good results, with finer packs for demanding products like film.
On speed: the shear-sensitivity rule translates to a maximum circumferential screw velocity of about 0.15 m/s. On a small screw that allows more RPM; on a 90 or 120 mm screw it caps the speed surprisingly low. The discipline is to accept it — pushing the screw faster trades product properties for output.
Temperatures: set by hardness
Extrusion temperatures track hardness — softer grades run cooler, harder grades hotter. Published guideline ranges:
| Shore hardness | Barrel [°C] | Adapter [°C] | Die head [°C] | Nozzle [°C] |
|---|---|---|---|---|
| 60–70 A | 140–175 | 160–175 | 165–170 | 160–165 |
| 75–85 A | 160–200 | 175–200 | 175–205 | 170–205 |
| 90–98 A | 170–210 | 200–220 | 195–215 | 190–210 |
| >98 A | 200–220 | 220–240 | 210–230 | 200–230 |
Two observations worth making. First, the spread across the hardness range is roughly 60 °C — a soft 65A tubing grade and a hard 55D profile grade are practically different materials at the temperature controller. Second, the profile rises from barrel toward die for the soft grades and flattens for the hard ones. As always, the specific grade's datasheet wins over any general table, and why hardness drives so much of TPU behavior is covered in understanding Shore hardness.
Melt pressure, power, and purging
A few machine-side numbers help set expectations:
- Melt pressure at the adapter typically runs 20–300 bar depending on head design, die gap, and melt temperature — but start-up peaks can reach 1,000 bar, which is why a continuously variable screw drive (or starve feeding) is recommended.
- Drive power: TPU needs a more powerful motor than most thermoplastics — power consumption runs about 0.3–1 kWh per kg of output depending on screw design. A melt pump has a proven record for smoothing melt flow.
- Purging: clean the extruder on material changes and after several days of continuous running. Polypropylene or HDPE — both of which tolerate high temperatures — are the usual purge materials, with a cleaning compound if needed.
Die design: long lands, no dead spots
The die rules follow from melt behavior. Flow channels should use small cross-sections that keep the melt moving uniformly and avoid dead spots — a die that flows everywhere is a die that self-cleans, while a stagnant corner is where degraded material accumulates and then sheds into the product as a streak or gel.
For tubing and profiles, dies with a relatively long land — two to four times the nozzle diameter — are recommended. The long land relaxes shear stresses before the melt exits, which buys consistent output and a calmer extrudate. Beyond those points, conventional thermoplastic die practice applies.
Cooling and calibration: the soft-melt problem
This is the part of the line where TPU differs most from rigid resins. The fresh extrudate has relatively low melt strength and distorts under its own weight, so cooling has to start immediately: the water bath close to the extruder head, with chilled water preferred (a spray-nozzle cooling line is a workable alternative). And because the soft material holds heat, the required bath length is generally greater than for other thermoplastics, growing with hardness, wall thickness, geometry, and haul-off speed.
Calibration has its own TPU twist: the active (vacuum) calibration used for most rigid thermoplastics does not work, because of TPU's high coefficient of friction — the extrudate grabs the calibrator instead of sliding through. Disc or sleeve calibration provides the guidance and support instead, and a lubricating film of water between extrudate and calibrator — typically from a water spray ring before the bath — is essential. It is the same high-friction, rubbery surface character that makes TPU grippy in service; here it just has to be managed instead of enjoyed.
Technique by product form
| Product | Technique notes |
|---|---|
| Tubing & profiles | Usually extruded horizontally; guide rollers in the bath matched to the shape; vacuum recommended to stabilize hollow profiles |
| Thin-wall tubing, fire-hose linings | Generally extruded vertically, with supportive air inside to keep the tube from collapsing |
| Cable & hose sheathing | Crosshead with a pressure or tubing die; the core being sheathed must be dry and grease-free to avoid blistering and ensure adhesion |
| Blown film | Specific film grades on a film-blowing head |
| Sheet / thicker flat film | Flat-film extrusion with a sheet die; standard extrusion grades suitable |
| Blow molding | Particular grades on conventional machines; roughened mold surfaces (~25–35 µm) ease demolding; wall-thickness control compensates parison stretch |
The sheathing note deserves emphasis because it fails quietly: a cable core that carries moisture or drawing grease will blister the jacket and kill adhesion, and no die or temperature setting will fix it. Core preparation is part of the extrusion process.
Coextrusion and foam extrusion
Two special methods extend what a TPU line can make:
- Coextrusion combines TPU with other thermoplastics in one step — a wear layer on a cheaper substrate, for instance. Good bonding requires compatible materials, and notably the compatibility can differ between polyester- and polyether-based grades, so the backbone choice (see polyester vs polyether TPU) reaches all the way into coextrusion planning.
- Thermoplastic foam extrusion reduces weight: chemical blowing agents in a conventional extruder reach foam densities of about 0.4–1.0 g/cm³, while physical gas injection goes below 0.4 g/cm³, with a nucleating agent to control cell structure.
Extrusion troubleshooting
Extrusion has its own defect list, and as with molding, the material side explains most of it:
| Symptom | First suspects |
|---|---|
| Output pulsation / throughput swings | Moisture; feed and melt pressure stability; screw speed |
| Die drooling | Insufficient pre-drying |
| Bubbles / blisters | Moisture in granulate (or a damp sheathing core) |
| Rough surface | Melt/die temperature; homogenization |
| Surface streaks | Contamination; degraded material from dead spots |
| Flow / spider lines | Die temperature; land length; homogenization |
Notice how many rows trace back to moisture. The drill is the same as molding — verify <0.02% before touching the line — and the full drying discipline is in drying TPU before molding. The molding-side defect logic, much of which transfers, is in processing window & common defects.
Bottom line
TPU extrudes well once the line respects three material facts. Because the melt is shear-sensitive, the screw does the work with geometry — a three-zone screw, L/D 25–30, compression near 1:2.5, circumferential speed held to about 0.15 m/s — not with RPM. Because the extrudate leaves the die with low melt strength, cooling starts at the head with chilled water, the bath runs longer than for other plastics, and calibration switches to disc or sleeve designs with a water film, since TPU's friction defeats standard vacuum calibration. And because the material is hygroscopic, anything pulsing, drooling, or blistering sends you back to the dryer first. Set temperatures by hardness from the grade's datasheet, give the die long lands and no dead spots, and the same material that jackets cable and lines fire hose will run steadily for days.
For grade-specific extrusion parameters and line design detail, BASF's Elastollan processing documentation is the reference this guide draws on.
FAQ
What screw is best for extruding TPU?
A single-screw extruder with a three-zone screw, L/D ratio of 25 to 30, and a compression ratio between 1:2 and 1:3 — preferably about 1:2.5 — is the common recommendation. Short screws with a high compression ratio are not suitable, because TPU is shear-sensitive.
What temperatures are used to extrude TPU?
It depends on hardness. Published guideline barrel ranges run from about 140–175 °C for soft 60–70 Shore A grades up to about 200–220 °C for grades above 98 Shore A, with adapter, die head, and nozzle zones set accordingly. Always follow the specific grade's datasheet.
Why does TPU need a longer cooling bath than other plastics?
Freshly extruded TPU has relatively low melt strength and distorts easily, so it needs effective cooling that starts close to the extruder head, preferably with chilled water. The required bath length is generally greater than for other thermoplastics and grows with hardness, wall thickness, and line speed.
Why can't standard vacuum calibration be used on TPU?
Because of TPU's high coefficient of friction, the active calibration used for most rigid thermoplastics does not work. Disc or sleeve calibration is used instead, and a lubricating film of water between the extrudate and the calibrator — often from a spray ring before the bath — is essential.
What causes die drooling and output variation in TPU extrusion?
Insufficient pre-drying is the classic cause. Moisture in the melt produces throughput variations and die drooling, along with bubbles and rough surfaces. TPU should be dried below 0.02 percent moisture before extrusion.
Can TPU be foamed in extrusion?
Yes. Chemical blowing agents in a conventional extruder reach foam densities of about 0.4 to 1.0 g/cm³, while physical blowing with gas injection reaches densities below 0.4 g/cm³, with a nucleating agent used to control the foam structure.
Related: TPU Processing Guide → · Drying TPU Before Molding →