Thermoplastic Polyurethane (TPU 88A)

Material Profile: Thermoplastic Polyurethane (TPU 88A) for Selective Laser Sintering

SLS Engineering Material Technical Report Series

Compiled from manufacturer technical datasheets and peer-reviewed literature

Abstract—Thermoplastic polyurethane for SLS (commercially Ultrasint TPU 88A from BASF Forward AM, also processed on EOS, 3D Systems and HP MJF equipment) is a soft elastomer powder enabling support-free fabrication of rubber-like geometries with full design freedom. Its block-copolymer structure — alternating hard segments (4,4'-MDI / chain extender) and soft segments (polyether or polyester polyol) — gives Shore A 88 hardness, ~360 % elongation at break, excellent abrasion resistance, hydrolysis resistance, and UV stability. SLS lattice geometries impossible to mould (e.g. Adidas 4DFWD midsoles) leverage TPU 88A's combination of energy return, fatigue resistance (validated > 100 000 cycles without crack growth), and the 80 % powder reusability typical of polyurethane SLS. Because TPU is an elastomer, the IEEE template's standard polymer tables are augmented with elastomer-specific rows (Shore A, tear strength, rebound, compression set) and the heat-deflection section is replaced by upper service-temperature notes.

Index Terms—additive manufacturing, selective laser sintering, SLS, thermoplastic polyurethane, TPU, TPU 88A, Ultrasint, elastomer, Shore A.

I.  MATERIAL IDENTIFICATION

This section establishes the canonical names and commercial designations under which the material is supplied.

A.  Designation

Trade names: BASF Forward AM Ultrasint TPU 88A (white / black variants); EOS TPU 1301; Lubrizol ESTANE 3D TPU M95A; Sinterit Flexa Performance / Flexa Bright. Shore hardness ranges from 60A (very soft) to 95A (semi-rigid); 88A is the consensus 'general-purpose' grade.

B.  Full Chemical Name

Thermoplastic polyurethane block copolymer. Hard segments are aromatic urethane (-NH-CO-O-) groups derived from 4,4'-methylene-diphenyl-diisocyanate (MDI) reacted with a short-chain diol (1,4-butanediol). Soft segments are polyether polyol (typically poly(tetramethylene glycol), PTMG, MW ~1 000–2 000) or polyester polyol; ether-based TPUs have superior hydrolysis resistance, ester-based TPUs have superior oil resistance.

C.  Aliases and Alternative Designations

Alias

Origin / Usage

TPU

Generic abbreviation for thermoplastic polyurethane

Ultrasint TPU 88A

BASF Forward AM commercial designation

TPE-U

Alternative thermoplastic-elastomer-urethane abbreviation

Estane

Lubrizol commercial TPU family

Desmopan

Covestro commercial TPU family

II.  COMPOSITION AND MOLECULAR STRUCTURE

A.  Empirical Chemical Formula

Block copolymer: ~[Hard - Soft - Hard - Soft]~_n where Hard = -(MDI-BDO)- urethane, Soft = -(O-(CH₂)₄)_x- ether. Hard segment fraction sets the Shore hardness — 88A corresponds to ~30 wt% hard segment.

Fig. 1.  Repeating unit / structural schematic of the polymer matrix.

Fig. 2.  Schematic of the single-phase polymer (no reinforcement).

B.  Composition Breakdown

TABLE I
 COMPOSITIONAL BREAKDOWN OF TPU (ULTRASINT TPU 88A, BASF FORWARD AM) (TYPICAL / PER SUPPLIER DATASHEET)

Constituent

Mass fraction

Function

TPU polymer powder (cryo- or co-extrusion-ground, d50 ≈ 60–80 µm)

≈ 99 wt%

Block-copolymer elastomer; hard:soft segment ratio sets Shore hardness

Anti-static / flow additives

< 0.5 wt%

Suppress powder triboelectric build-up; aid recoating

UV / heat stabilisers

< 0.5 wt%

Inhibit photo-oxidation and thermal yellowing

Total

100 wt%

—

III.  MECHANICAL PROPERTIES — XY BUILD DIRECTION (HORIZONTAL)

In the XY orientation the tensile load is applied parallel to the powder-bed plane (in-plane). For polymer SLS this is typically the stronger orientation due to better neck formation between particles within a single layer; for metal DMLS/SLM, columnar β / α-grain growth perpendicular to the build direction also yields different anisotropy that is partially relieved by post-build heat treatment (e.g. stress-relief, HIP).

TABLE II
 MECHANICAL PROPERTIES — XY ORIENTATION (TPU (ULTRASINT TPU 88A, BASF FORWARD AM))

Property

Value (XY)

Test method / source

Density (sintered part)

≈ 1.10 g/cm³

ISO 1183

Shore A hardness (NOT Shore D — elastomer)

≈ 88 A

ASTM D2240 / ISO 7619-1

Tensile strength, ultimate (UTS)

≈ 8 MPa (1 160 psi)

ASTM D638 / ISO 37 (rubber tensile)

Tensile (Young's) modulus

≈ 85 MPa (12 328 psi) — initial / 100% modulus

ASTM D638 — note that for elastomers 'modulus' often refers to stress at given elongation

Elongation at break

≈ 360 %

ASTM D638 — characteristic of soft elastomers

Tear strength (Type C)

≈ 50–60 N/mm

ASTM D624 / ISO 34-1 — relevant elastomer metric

Compression set, 23 °C / 22 h

≈ 30 %

ISO 815 — recovery after sustained compression

Bayshore rebound (resilience)

≈ 50 %

ASTM D2632

Abrasion loss (DIN 53516)

≈ 60 mm³

DIN 53516 — lower is better

IV.  MECHANICAL PROPERTIES — Z BUILD DIRECTION (VERTICAL)

In the Z orientation the tensile load is applied perpendicular to the powder layers; failure occurs across inter-layer fusion bonds. For polymer SLS the Z properties are typically 70–90 % of XY; for metal LPBF (laser powder-bed fusion) processes Z elongation is often higher due to the columnar grain structure but UTS / yield can be slightly lower in the as-built state. Heat treatment (anneal, HIP) reduces the anisotropy substantially.

TABLE III
 MECHANICAL PROPERTIES — Z ORIENTATION (TPU (ULTRASINT TPU 88A, BASF FORWARD AM))

Property

Value (Z)

Test method / source

Density (sintered part)

≈ 1.10 g/cm³

ISO 1183

Shore A hardness

≈ 88 A

ASTM D2240 — orientation-independent for hardness

Tensile strength, ultimate (UTS)

≈ 6 MPa (estimate, ≈ 75 % of XY)

ASTM D638 — Z weaker due to inter-layer fusion

Elongation at break

≈ 270 % (estimate, ≈ 75 % of XY)

ASTM D638 — Z elongation reduced

Tear strength (Type C)

≈ 35–45 N/mm (estimate)

ASTM D624

Elastomer SLS parts retain useful Z-direction strength because the laser fully melts the powder rather than sintering — but Z-direction elongation drops by ~25 % because elastomer chain entanglement does not fully transfer across the layer interface during the very brief melt window. For repeated-flexing applications (footwear, gaskets), orient parts so the dominant strain axis lies in-plane.

V.  RECOMMENDED PROCESS PARAMETERS

Values summarised below give consensus operating windows from public datasheets (EOS, 3D Systems, BASF Forward AM, SLM Solutions). Specific machines and parameter sets may differ within ±10 %; the supplier's verified parameter sheet always supersedes this table.

TABLE IV
 RECOMMENDED LASER POWDER-BED-FUSION PROCESS PARAMETERS FOR TPU (ULTRASINT TPU 88A, BASF FORWARD AM)

Parameter

Range

Notes

Laser type & wavelength

CO₂ laser, 10.6 µm

TPU absorbs less efficiently than PA12; higher power required

Laser power (typical)

30–55 W

Higher than PA12 to overcome lower IR absorptivity

Scan speed

5 000–8 000 mm/s

Lower than PA12; longer dwell improves chain mobility

Layer thickness

100–120 µm

BASF recommends 0.10 mm

Powder-bed (build-chamber) temperature

120–135 °C

Lower than PA12 because TPU melts at lower temperature (~165 °C peak)

Removal-chamber temperature

100–110 °C

Slow cooldown to avoid distortion of soft parts

Inert atmosphere

Nitrogen, O₂ < 1 %

Prevents oxidative chain scission and yellowing

Powder refresh ratio (used : virgin)

≈ 80 : 20 (high reusability)

TPU SLS allows up to ~80 % reuse — a major economic advantage over PA12

VI.  GLASS TRANSITION TEMPERATURE (TG)

Reported / typical Tg: ≈ -30 to -40 °C (soft segment Tg).

TPU has two thermal transitions: soft-segment Tg (≈ -35 °C, sets low-temperature flexibility) and hard-segment dissociation (~150–180 °C, sets upper service limit). HDT in the conventional 0.45 / 1.82 MPa sense is not normally reported for elastomers — instead, upper service temperature (~80 °C continuous) and Vicat softening point (~85 °C) are used.

VII.  HEAT DEFLECTION TEMPERATURE (HDT)

Heat deflection temperature is the temperature at which a standard bar deflects 0.25 mm under a specified flexural load (ASTM D648 / ISO 75).

TABLE V
 HEAT DEFLECTION TEMPERATURE OF TPU (ULTRASINT TPU 88A, BASF FORWARD AM) UNDER STANDARD TEST LOADS

Test load

HDT

Standard / source

0.45 MPa

Not normally reported for soft elastomers (≈ 80 °C upper continuous service)

Vicat softening B/50 N substituted; ASTM D1525 / ISO 306

1.82 MPa

Not applicable (elastomer collapses under this load)

—

VIII.  DISTINGUISHING CHARACTERISTICS AND STANDARDS

A.  Elastomer mechanical regime

Shore A 88, elongation at break ≈ 360 %, tensile strength ≈ 8 MPa. Unlike rigid SLS thermoplastics, TPU 88A is governed by elastomer mechanics: the strain-energy release from a stretched part can exceed 50 % (Bayshore rebound), making it ideal for energy-return applications (Adidas 4DFWD midsoles, athletic footwear). Conventional UTS/modulus comparisons with PA12 are misleading — the figures of merit are tear strength, compression set, and rebound.

B.  Hydrolysis and UV resistance

Ether-based TPU formulations (Ultrasint TPU 88A) show hydrolysis resistance superior to ester-based TPUs and PA-based elastomers — relevant for outdoor wearables, footwear, and humid-environment seals. UV resistance is good for white grades (when stabilised); black grades (TPU 88A black) are best for sustained outdoor exposure.

C.  Fatigue resistance

Validated to > 100 000 flex cycles (Ross flex / De Mattia flex equivalent) without crack initiation, enabling lattice midsoles, gaskets, and seals in high-cycle applications. Fatigue resistance is enabled by the TPU phase morphology — physical (not chemical) crosslinking via hard-segment domains acts as crack-bridging.

D.  Skin-contact biocompatibility

Ultrasint TPU 88A passes ISO 10993-5 (cytotoxicity) and ISO 10993-10 (skin sensitisation), supporting wearable, sports protection, and orthotic applications. Not certified for long-term implant contact.

E.  High powder reusability — economic advantage

BASF and EOS report up to 80 % reuse of un-sintered TPU 88A powder (typical refresh: 80 % used + 20 % virgin), vs ~50 % for PA12. This dramatically lowers per-part material cost and is one of the principal reasons for the rapid growth of TPU SLS for end-use parts.

IX.  REPRESENTATIVE APPLICATIONS

TPU (Ultrasint TPU 88A, BASF Forward AM) is typically deployed in the following applications:

1)  Athletic footwear midsoles: Lattice midsoles in shoes such as the Adidas 4DFWD — geometry tuned to deliver direction-specific energy return impossible with conventional EVA foam moulding.

2)  Gaskets, seals, and dampers: Custom geometries (single-piece hex-cell vibration isolators, segmented seals) for low-volume industrial machinery and motorsport.

3)  Wearable orthoses and prosthetic interfaces: Patient-specific cushioning layers with skin-contact biocompatibility — replaces silicone moulding for prosthetic socket liners.

4)  Protective sports equipment: Helmet liners, shin / elbow / knee pads with topology-optimised lattice cores — energy absorption per unit mass exceeds moulded EVA.

5)  Soft robotics actuators and grippers: Compliant pneumatic actuators and food-handling grippers exploiting the elastomer's reversible large-strain regime.

X.  REFERENCES

[1]  BASF Forward AM, “Ultrasint TPU 88A — Technical Data Sheet, Version 2.2,” 2021. [Online]. Available: https://forward-am.com/wp-content/uploads/2021/04/BASF_3DPS_TDS_Ultrasint-TPU-88A.pdf

[2]  BASF Forward AM, “Ultrasint TPU 88A — Datasheet & application notes.” [Online]. Available: https://forward-am.com/material-portfolio/ultrasint-tpu-88a/

[3]  Sculpteo, “SLS TPU 88A — Material reference,” 2024. [Online]. Available: https://www.sculpteo.com/en/materials/sls-material/tpu88a/

[4]  Forge Labs, “TPU 88A — Flexible Thermoplastic Elastomer,” Technical reference. [Online]. Available: https://forgelabs.com/3d-printing/materials/tpu-88a

[5]  Sinterit, “Flexa Performance — durable & flexible TPU for SLS,” Technical bulletin. [Online]. Available: https://sinterit.com/materials/flexa-performance/

[6]  ASTM D638-14, “Standard Test Method for Tensile Properties of Plastics,” ASTM International, West Conshohocken, PA, 2014.

[7]  ASTM D790-17, “Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics,” ASTM International, 2017.

[8]  ASTM D256-10, “Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics,” ASTM International, 2018.

[9]  ASTM D648-18, “Standard Test Method for Deflection Temperature of Plastics Under Flexural Load,” ASTM International, 2018.

[10]  ISO 527-2:2012, “Plastics — Determination of tensile properties — Part 2,” ISO, Geneva, 2012.

[11]  ASTM D2240-15, “Standard Test Method for Rubber Property — Durometer Hardness,” ASTM International, 2015.

[12]  ASTM D624-00(2020), “Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers,” ASTM International, 2020.

[13]  ASTM D2632-15, “Standard Test Method for Rubber Property — Resilience by Vertical Rebound,” ASTM International, 2015.

[14]  ISO 815-1:2019, “Rubber, vulcanized or thermoplastic — Determination of compression set,” ISO, 2019.

(Image Resouce: Forgelabs)