Essentium TPU 90A Additive Manufacturing Filament is a segmented thermoplastic polyurethane monofilament supplied in nominal diameters of 1.75 mm and 2.85 mm with a Shore hardness of 90A measured according to ISO 868. Manufacturer-published density values are 1.18 g/cm³ to 1.22 g/cm³ under ISO 1183-1. Tensile strength at break lies in the 30 MPa to 40 MPa range when tested as a Type IV specimen under ASTM D638-14, with elongation at break in the 450% to 600% range. The low flexural modulus, typically below 150 MPa under ISO 178, separates the material from rigid AM polymers such as PLA and PETG, while the 90A Shore hardness distinguishes it from softer 60A or 70A TPU grades. The filament is therefore intended for fused filament fabrication of void-filling gaskets, protective bellows, cable strain-relief components, vibration isolators, and wear-tolerant sleeves that require repeated flexural recovery rather than high static stiffness.

The product is typically supplied on vacuum-sealed spools with desiccant. Dimensional tolerance is held to ±0.05 mm for both filament diameters, and feed-path monitoring is recommended because the elastomer buckles more readily than rigid filament when extruder idler pressure is excessively high. On production-scale filament extrusion lines, batch-to-batch Shore hardness is controlled by blending pellet feedstock with melt flow index variation within ±15%. Twin-screw extruders with L/D ratios of 24:1 to 30:1 and gear pumps are used to maintain ovality and diameter consistency. Nozzle pressure fluctuations greater than 0.5 MPa during downstream fused filament fabrication may indicate non-uniform melt quality, moisture contamination, or feed-gear slip.

Moisture control is a primary process boundary. The polymer is hygroscopic, and exposure at relative humidity above 40% can increase absorbed water above 0.2%. At melt temperatures, residual moisture hydrolyzes urethane linkages, producing molecular weight loss that appears as nozzle surging, surface roughness, and poor interlayer fusion. A desiccant dryer with a dew point below -40°C is specified for 4 h at 70°C or 2 h at 80°C once the spool has been outside sealed packaging for more than 24 h. In print farms where multiple fused filament fabrication systems operate in unconditioned space, unsealed spools stored at relative humidity above 60% require containment with activated alumina or molecular sieve desiccant. Feeding moist filament into a direct-drive extruder at 235°C can generate steam bubbles within the nozzle, causing intermittent extrusion and weak weld lines.

What extrusion and moisture parameters define the 90A processing window?

Extrusion temperatures between 220°C and 240°C are used for a 0.4 mm nozzle. The lower bound is set by melt viscosity and insufficient interlayer diffusion; the upper bound is limited by thermal degradation of urethane linkages and emission of acrid decomposition products. A build plate temperature between 40°C and 60°C is sufficient for first-layer adhesion on polyimide tape, polyetherimide sheet, or glass with polyvinyl alcohol adhesive. An actively heated enclosure is not required for small parts, but tall sections exceeding 100 mm in the Z-axis benefit from a passively heated chamber at 30°C to 40°C to reduce differential shrinkage. Because the filament is a flexible elastomer, a direct-drive extruder is preferred. Bowden systems are limited to print speeds below 20 mm/s; direct-drive systems can operate from 25 mm/s to 40 mm/s without excessive filament buckling. Retraction distance should be reduced to 0.5 mm to 1.5 mm for direct-drive and 2 mm to 3 mm for short Bowden paths, with retraction speed below 20 mm/s. Long retraction pulls air into the melt zone and promotes filament compression and nozzle clogging.

Volumetric throughput is another limiting factor. For 1.75 mm filament extruded through a 0.4 mm nozzle, the stable flow rate is between 4 mm³/s and 6 mm³/s. Above this range, melt pressure rises sharply, causing feed gear slip and melt leakage around the hot-end heat break. Hardened steel or stainless steel nozzles are specified because tungsten carbide nozzles may generate excessive shear heating in this viscoelastic melt, although published data for this specific configuration is limited. A nozzle temperature tower should be run for each supplier lot because Shore hardness and melt flow index vary within the 90A specification band.

Melt flow index of TPU 90A measured under ISO 1133-1:2022 at 190°C with a 21.6 kg load is typically below 10 g/10 min, indicating high viscosity relative to PLA. Direct-drive systems with dual-drive extruders should reduce idler pressure to prevent filament deformation. Excessive idler compression increases feed resistance and can generate filament shavings that accumulate in the drive gear. The melt is also sensitive to residence time. At temperatures above 240°C, prolonged residence in the hot end can shift Shore hardness upward and reduce elongation by promoting crosslinking or chain scission, depending on antioxidant package and moisture content.

Interlayer adhesion is the limiting mechanical variable rather than bulk tensile strength. When printed specimens are tested under ASTM D638-14, Z-direction tensile strength is typically 50% to 80% of XY-direction strength depending on layer height, extrusion multiplier, and cooling fan speed. Layer heights from 0.10 mm to 0.20 mm are used for sealing surfaces. Cooling fans should not exceed 30% for most geometries because excessive surface cooling reduces interlayer diffusion and creates delamination. For dynamic seals and low-pressure gaskets, seam placement should be rotated or randomized to avoid a continuous leak path. Minimum wall thickness for an unreinforced low-pressure gasket is 1.5 mm; thinner sections require higher Shore hardness or composite reinforcement.

Support structures are difficult to remove from TPU because of localized fusion and deformation during breakaway removal. Soluble support materials are preferred for complex channels and internal cavities. Breakaway supports require shear cuts and are limited to accessible external surfaces. For overhangs, layer times below 10 s can lead to sag and loss of dimensional accuracy. Bridge performance is poor; unsupported bridge lengths above 5 mm usually require supports. Infill patterns with low in-plane connectivity, such as lines or gyroid, are used to retain compliance. Solid walls and high infill above 60% rapidly increase stiffness and reduce elastic recovery.

Stringing and surface defects are controlled by travel speed, wipe moves, and coast settings. TPU forms melt bridges across travel moves because of its high elongation and low modulus. Travel speed should be set between 150 mm/s and 250 mm/s, with wipe moves enabled where possible. Z-hop above 0.2 mm may cause nozzle ooze and surface hairs. Extra prime amount after retraction should be set between 0.05 mm³ and 0.1 mm³ to compensate for melt compression. Combing within skin can reduce visible travel artifacts but may also create heat concentration near thin walls.

When 90A Shore hardness is specified instead of rigid PLA, PETG, or ABS

Rigid AM materials such as PLA and PETG have tensile elongation below 25% and fail before 50% strain under ASTM D638-14. Essentium TPU 90A accepts repeated flexure with high elastic recovery. The substitution is therefore appropriate for cable strain-relief glands, pneumatic actuator bellows, vibration isolators, and conveyor scraper edges. Under cyclic loading, however, TPU exhibits hysteresis, internal heat generation, and compression set. Clamped assemblies must be designed for stress relaxation, because a fixed displacement clamp will lose sealing force over time. The product is not a direct substitute for rigid fixtures when dimensional stability under load is required.

The flexural modulus of 90A TPU is generally below 150 MPa under ISO 178, compared with 2000 MPa to 3500 MPa for PETG and PLA. Stiffness can be restored by embedding rigid inserts, increasing wall thickness, or printing a rigid skeleton and overmolding with TPU. Compared with a Shore 95A TPU, this grade has lower hardness and higher elongation; compared with Shore 85A TPU, it has higher abrasion resistance and a wider extrusion window because of higher melt viscosity. The choice between polyester-based and polyether-based TPU also affects hydrolysis and oil resistance. The Essentium datasheet should be consulted for backbone chemistry, because polyether grades offer better hydrolysis resistance in humid environments while polyester grades offer better resistance to non-polar oils and fuels.

The main alternative flexible AM products are Shore 85A, 95A, and Shore 74D TPU grades, thermoplastic copolyesters, and styrenic block copolymers. Compared with Shore 85A TPU, the 90A grade has higher stiffness and better feed reliability; compared with Shore 95A, it has lower durometer and higher elongation. Compared with thermoplastic copolyester elastomers such as Shore 40D to 72D, the TPU has lower print temperatures and softer surface but lower temperature resistance. Compared with silicone thermoset elastomers, the TPU cannot match 200°C continuous service or autoclave stability and requires a thermoplastic processing route.

Chemical compatibility follows polyurethane behavior. The filament resists non-polar oils, greases, and aliphatic hydrocarbons but is swollen by ketones, esters, chlorinated solvents, and strong acids. Continuous service temperature is usually bounded by Vicat softening near 80°C under ISO 306 A50, with low-temperature flexibility potentially retained to -40°C depending on backbone chemistry. For clamped seals exposed to heat, compression set should be measured under ASTM D395-18 Method B at the expected service temperature. Creep compliance under ASTM D2990 is required if load retention is critical.

Low-pressure pneumatic seals, bellows for linear rails, cable grommets, and vibration isolators are produced from the grade. Under ISO 815-1 compression set tests, TPU 90A can show 20% to 40% permanent set after 22 h at 70°C depending on formulation. This means dynamic seals require periodic retightening or spring washers. Abrasion loss under ISO 4649 A is usually below 50 mm³, making the material suitable for conveyor scrapers and guides. Tear strength measured under ISO 34-1 B is in the 50 kN/m to 90 kN/m range, which supports edge-loaded gasket retention.

Compliance, safety, and continuous service limits

Regulatory compliance for raw resin may include REACH and RoHS 2011/65/EU, but printed parts are not automatically compliant with FDA 21 CFR food-contact provisions. Users requiring medical or food-contact status must validate the printed article after processing because additives, colorants, and surface porosity can affect migration behavior. Thermal decomposition at temperatures above 250°C generates isocyanate decomposition products. Local exhaust ventilation is required when processing in enclosed areas. The safety data sheet for the specific product must be consulted for exposure limits and emergency procedures. Waste filament and purge material are not compostable; disposal should follow local thermoplastic waste regulations.

On production fused filament fabrication lines, the material is used for low-pressure gaskets and protective bellows. A representative configuration uses a direct-drive extruder with a 0.4 mm hardened steel nozzle, a 0.2 mm layer height, and 235°C extrusion temperature. Gaskets with 2 mm wall thickness are printed with 100% infill and random seam placement. For repeatable clamping, the design should include a compressible rib rather than relying on continuous foam texture. Published data for this specific configuration is limited; users should validate compression set under ASTM D395-18 Method B at service temperature, because TPU loses sealing force if initial compression exceeds 25% and the service temperature remains above 60°C for extended periods.