BASF 3D Ultrafuse TPU 85A Fused Filament is a segmented thermoplastic polyurethane feedstock produced for fused filament fabrication platforms. The product is available in nominal diameters of 1.75 mm and 2.85 mm with a stated diameter tolerance of ±0.05 mm and is packaged on 750 g spools. The material is classified as an elastomeric thermoplastic rather than a rigid amorphous or semi-crystalline polymer. It is intended for direct-drive and suitably constrained Bowden-type material feed systems operating with nozzle orifices of at least 0.4 mm. The supplier technical datasheet lists a density of 1.16 g/cm³ under ISO 1183-1 and a nominal Shore A hardness of 85 under ISO 7619-1.

The polyurethane architecture comprises alternating hard aromatic diisocyanate-based domains and soft polyol-derived domains. The hard domains act as reversible physical crosslinks that soften during extrusion and re-form during cooling. This arrangement provides elastomeric recovery at room temperature while retaining melt processability. In similar segmented polyurethane formulations, differential scanning calorimetry reveals a broad hard-domain melting endotherm in the region of 160–190 °C; published thermal data for this specific grade is limited to the recommended extrusion temperature and storage conditions. Because the soft segment is not explicitly designated in the general technical datasheet as either polyether or polyester, chemical resistance and hydrolytic ageing behaviour should be confirmed against the manufacturer’s current technical and regulatory documentation.

The 85A hardness value places the material in the flexible-elastomer range. It is softer than 95A TPU and considerably softer than rigid acrylonitrile-butadiene-styrene or polylactic acid feedstocks. The product is therefore specified only where compliance, energy return, or conformability is the principal design requirement. Batch-to-batch hardness variation should be checked against the supplier’s release documentation; typical Shore A batch tolerance for this class of polyurethane is controlled to approximately ±3 Shore A units under ISO 7619-1, though the specific release range must be obtained from the manufacturer.

The filament is manufactured to a circular cross-section with low ovality. For flexible feedstocks, ovality above the stated tolerance is a known cause of feed-roller slip because the effective diameter changes as the filament rotates through the constraining path. Incoming inspection should therefore include diameter measurement at multiple angular positions using a dual-axis laser micrometer. Diameter excursions outside ±0.05 mm can produce over- or under-extrusion at the nozzle, particularly at the lower end of the recommended print speed range.

Unopened spools should be stored in sealed packaging at 15–25 °C and below 50% relative humidity. Shelf life for polyurethane filaments is commonly limited by moisture uptake and additive migration rather than chain scission at ambient temperature. If the filament becomes brittle, discolours, or emits a sharp odour during extrusion, the material may have been thermally degraded and should not be processed.

Which standardised mechanical values and test methods apply to the 85A grade?

Published values are typical data derived from standardised specimens and are not guaranteed production-lot specifications. They should be used for material selection, not as a replacement for end-part testing. The following values are reproduced from the manufacturer’s technical datasheet for dry filament.

The tensile values are conventionally measured on ISO 527-2 specimens. In fused filament fabrication components, the effective mechanical response is anisotropic because layer interfaces represent planes of reduced polymer diffusion. A part loaded normal to the build direction typically exhibits lower tensile strength and lower elongation than the datasheet XY-direction values. Z-direction interlayer adhesion is process-dependent and is not fully represented by standard feedstock data. For sealing and pressure-bearing components, the load path should be oriented in the XY plane, and Z-axis performance should be validated on the target printer using product-specific test pieces.

The elastomeric nature of the material means that standard uniaxial tensile testing is strain-rate dependent. At low strain rates the soft segments relax and the material appears more compliant; at high strain rates the hard domains do not fully relax and the apparent stiffness increases. For vibration isolation, compression pads, and impact-absorption elements, the intended service strain rate should therefore be matched with the testing speed under ISO 527-2 or ISO 37.

Hardness is measured on the printed or injected surface and is not equivalent to part stiffness. Thin walls with low infill density can deform at far lower force than the Shore A value implies. For compression elements, the compressive force-deflection response should be measured on the actual printed geometry under ISO 7743 or a similar compression standard, because layer height, infill pattern, and wall count alter the macroscopic stiffness independently of the bulk polymer hardness.

Filament drying is specified at 60 °C for 4 h in a forced-air or vacuum dryer after ambient moisture exposure. At relative humidity above 60%, the polar soft segments of the polyurethane absorb atmospheric water. Residual moisture reaches the hot end and flashes into steam, creating voids at the layer interfaces and reducing melt strength. The result on production-scale machines is intermittent extruder throughput, audible outgassing at the nozzle, and low Z-direction tensile strength. Dried spools should be processed from sealed containers or maintained in a dry-feed filament dryer at approximately 50 °C during long build cycles.

Moisture-induced defects are not evidence of material contamination. They are reversible by re-drying, provided the filament has not been thermally degraded. A heavily saturated spool may require drying beyond the 4 h baseline; the moisture content can be monitored gravimetrically by weighing a small sample before and after drying. Silica-gel desiccants are adequate for sealed container storage below 50% relative humidity at 15–25 °C.

Extrusion, build plate, and motion constraints on direct-drive and Bowden systems

Extrusion temperature is specified in the range 210–240 °C, with 225 °C recommended as a starting point on a 0.4 mm brass nozzle. The build plate temperature can be set between 20 °C and 60 °C. Print speed for direct-drive systems with a constrained filament path can be increased to 40 mm/s; Bowden tube layouts require a reduction to 15–25 mm/s because the flexible filament column buckles under the compressive force required to push through the tube. The nozzle orifice should not be below 0.4 mm, as smaller orifices increase melt pressure and shear heating, leading to feed roller slippage and hardness shift from polymer degradation.

Retraction distance should be kept at or below 2 mm, and retraction speed should be limited to prevent drawing air into the melt chamber. On direct-drive extruders with spring-loaded idler arms, the idler tension should be reduced to the minimum that prevents free-slip; excessive idler compression deforms the filament from round to oval and can wedge the feed path below the heat break. First-layer height should be set to 0.10–0.20 mm for a 0.4 mm nozzle to increase contact area and reduce delamination risk.

Because the extrusion temperature is low relative to semi-crystalline engineering filaments, heat creep into the feed zone can soften the filament prematurely. All-metal hot ends with adequate cold-end cooling are preferred over PTFE-lined hot ends for long runs. If the heated block is held at 225 °C without active cooling for an extended idle period, the filament above the heat break can soften and bind; a purge after idle periods longer than 10 minutes is therefore standard practice on production cells.

A heated chamber is not required. Glass and polyetherimide build surfaces with a polyvinylpyrrolidone-based adhesive provide adequate first-layer anchoring within the specified bed-temperature window. On unheated or low-temperature beds, the first layer may delaminate if the build plate is not cleaned with anhydrous isopropanol before printing. For continuous production, the build plate should be cooled to ambient before flexible parts are removed; the high elongation of the TPU resists brittle failure during peel-off but can stretch thin walls and distort geometry if removal force is applied unevenly.

Supports are difficult to remove from flexible TPU because the material tears or stretches rather than snapping at the interface. Self-supporting designs with shallow overhangs are preferred. Where supports are unavoidable, breakaway interface layers should be tested first; dual-extruder soluble support materials can be used only if the support polymer is compatible with the TPU processing window and does not require bed temperatures above 60 °C. Post-print annealing is not a standard procedure for this grade; published data on thermal annealing of fused filament fabricated 85A TPU is limited.

The practical maximum volumetric flow rate is determined by filament column strength and heater power rather than by a single datasheet value. On flexible feedstocks, excessive back-pressure can cause the hobbed gear to tear the filament instead of pushing it. The maximum stable throughput must therefore be established on the target production platform by incremental flow-rate testing under the selected nozzle temperature and layer height.

When flexible 85A polyurethane replaces rigid ABS or 95A TPU in service

Compared with a 95A TPU filament, the 85A grade provides lower Shore hardness, lower tensile strength, and lower abrasion resistance, but it can accommodate higher elongation and lower-force flexural recovery. Compared with rigid ABS or PLA, the TPU exhibits elongation above 620% under ISO 527-2 and is selected only when the part must flex, stretch, damp vibration, or maintain conformal contact. Rigid feedstocks are used where tensile modulus, dimensional accuracy under load, and low cost per static part dominate.

Supplier literature lists the material for protective bellows, dust covers, damping pads, shoe midsoles, gripper fingertips, cable grommets, low-pressure gaskets, and flexible snap-fit segments. In sealing applications, the contact face should be printed in the XY plane. Fused filament fabrication layer lines create a potential leak path along the Z direction unless the part is post-processed or the wall count and extrusion multiplier are increased. For dynamic flexure, service life depends on layer orientation, surface finish, and strain amplitude; no universal fatigue limit is supplied with the standard datasheet.

The material differs from rigid Ultrafuse grades not primarily in melt temperature but in deformation behaviour after printing. Rigid feedstocks fail at low strain; TPU 85A sustains high elongation but lacks the modulus required for static structural frames. In assemblies, rigid components can be combined with TPU sections through interlocking geometry or adhesive bonding, but direct chemical bonding to ABS and PLA in a multi-material build is not guaranteed because the polymers have different thermal expansion coefficients and surface energies. Where multi-material adhesion is required, lap-shear testing under ISO 4587 is recommended on the target material combination.

Chemical resistance of thermoplastic polyurethane generally includes dilute aqueous solutions, oils, and aliphatic hydrocarbons. Aromatic solvents, ketones, strong acids, and strong oxidisers can swell or degrade the soft and hard domains. Before deployment, immersion testing under ISO 175 or ISO 1817 should be performed using the target chemicals at the service temperature. Continuous load-bearing service at elevated temperature should be validated by compression-set testing under ISO 815-1 because the thermoplastic hard domains soften as temperature increases. Published data for cyclic fatigue, hydrolytic ageing, or creeping-flow performance of fused filament fabricated 85A TPU in this specific configuration is limited.