BASF 3D Ultrafuse PET fused filament is a polyethylene terephthalate homopolymer monofilament produced for open-frame fused filament fabrication machines. The product is supplied in 1.75 mm and 2.85 mm diameters on 750 g net-weight spools, vacuum-sealed with desiccant to limit moisture uptake during storage. Published density under ISO 1183-1:2012 is 1.27 g/cm³. The thermal profile obtained by differential scanning calorimetry shows a melting onset near 238 °C and a melting peak near 245 °C under ISO 11357-3. The grade is intended for dimensionally stable technical parts, fixtures, covers, jigs, and functional prototypes where low warpage and moderate service temperature are more important than high-impact toughness. Unlike filled polyester compounds, this feedstock does not require an abrasive-resistant nozzle or a heated build chamber, although a heated platform is required to manage first-layer solidification strain.

Diameter control and spooling are critical because monofilament ovality above 0.05 mm can generate cyclic extruder flow fluctuations in a 0.4 mm nozzle at fixed feed rate. The manufacturer applies closed-loop dual-axis laser micrometry during winding to maintain dimensional consistency. A full-spool run with a 0.20 mm layer height and 40 mm/s print speed therefore produces a more uniform bead than unstabilized PET monofilament. On direct-drive printers, spool drag should remain below 2 N to avoid skipped steps in the extruder gear.

On a standard Cartesian or CoreXY printer with a 0.4 mm brass nozzle, the processing window typically spans an extrusion temperature of 235–250 °C and a build surface temperature of 60–80 °C. Direct-drive extruders can use retraction distances of 1–3 mm, while Bowden configurations may require 4–6 mm to reduce oozing without causing nozzle plugging. Layer heights between 0.10 mm and 0.20 mm with line widths of 0.38–0.45 mm are used for structural specimens. Build surfaces of PEI, polycarbonate, or coated glass at the upper bed-temperature limit improve first-layer peel resistance. On open-frame equipment, warping is lower than unfilled polypropylene or polycarbonate under identical bed adhesives, but published quantitative warp values for this specific filament configuration are limited. A closed chamber is not required, and ambient room conditions of 20–25 °C produce acceptable results when draughts are eliminated.

What Limits the Service Temperature of Ultrafuse PET After Printing?

The load-bearing temperature boundary is governed by heat deflection temperature and Vicat softening data. Manufacturer-published typical values give heat deflection temperature of 75 °C under 0.45 MPa flexural stress using ISO 75-2:2013 method B and Vicat softening of 78 °C under method A50 of ISO 306:2013. As-printed PET homopolymer therefore should not be specified for continuous mechanical load above 60–65 °C, particularly when the part is constrained by metal fasteners with a higher thermal expansion coefficient. Recrystallization during annealing at 110 °C may raise dimensional stability but can embrittle the amorphous tie-chain network. This distinguishes it from polycarbonate and polysulfone grades, which retain load-bearing capacity above 100 °C under ISO 75-2 method A. Applications involving hot air ducts, underhood brackets, or steam-sterilized medical tools exceed the product’s thermal boundary.

The product also differs from carbon-fibre-reinforced PET grades in that no fibre reinforcement is present. This permits continuous printing with a standard brass nozzle and avoids severe abrasive wear, but it lowers stiffness and creep resistance. A fibre-filled PET filament would typically provide higher tensile modulus and lower thermal expansion, whereas the unfilled homopolymer remains more suitable for translucent parts and geometries where fibre orientation would introduce anisotropic shrinkage.

Drying Thresholds, Moisture Uptake, and Hydrolysis Risk

PET homopolymer is hydrolytically sensitive in extrusion. Moisture absorbed from ambient air reacts with ester linkages during heating, reducing melt viscosity and producing gaseous voids at the nozzle. The manufacturer’s handling instructions recommend drying at 60–65 °C for 4 h in a forced-air oven or filament dryer before printing if the spool has been removed from its sealed package for more than 24 h at 50% RH or higher. After drying, the filament should be held in a sealed desiccant box with a dew point below -30 °C or printed within 8 h in a conditioned room. Failure to dry manifests as intermittent extrusion, splayed first-layer lines, and a reduction in Z-axis tensile strength because vapour bubbles create microvoids between deposited beads. Storage at 15–30 °C and relative humidity below 20% is recommended for unopened spools. Visual transparency of the natural grade does not provide a reliable moisture indicator because haze often develops only after hydrolysis has begun.

Tensile and flexural properties reported by the manufacturer under ISO 527-2 using dried specimens include tensile modulus of 2100 MPa, tensile stress at yield of 49 MPa, nominal strain at break of 16%, flexural modulus of 2000 MPa under ISO 178, and notched Charpy impact strength of 4 kJ/m² under ISO 179-1. These values refer to bulk or well-fused XY-plane samples and do not transfer directly to the interlayer interface. In fused filament fabrication, Z-axis tensile strength is commonly 40–60% of the XY-plane value because incomplete polymer chain diffusion across the weld interface limits the through-thickness load path. Users who require Z-axis certification should generate specimens according to ISO 527-2 type 1BA at the intended layer height, print speed, and chamber conditions, since published data for this specific configuration is limited.

When layer welding is optimized, the natural grade can produce translucent sidewalls, though printed translucency declines with layer height and moisture. Interlayer weld strength is rate-dependent: higher extrusion temperature and lower print speed increase polymer chain interdiffusion across the interface. A nozzle temperature of 250 °C at 30 mm/s generally yields better through-thickness strength than 235 °C at 60 mm/s, but stringing and dimensional softening may increase. Operators should validate the weld factor using a flat tensile bar printed in the Z orientation rather than relying on visual sidewall quality.

When the Part Must Resist Impact, Ultrafuse PET Is Not a Drop-In Replacement for PETG

The homopolymer backbone differs from glycol-modified PET copolyesters in crystallinity, fusion behaviour, and impact response. PETG filament grades typically incorporate cyclohexanedimethanol at 15–30 mol%, which suppresses crystallinity and produces notched Charpy impact values in the 8–10 kJ/m² range under ISO 179-1. BASF Ultrafuse PET reports a notched Charpy impact average near 4 kJ/m², reflecting the more ordered microstructure. The same ordering gives the homopolymer a higher modulus and better surface hardness after annealing, but it reduces tolerance to sharp radius changes, threaded inserts, and snap-fit deflection. Designers moving from PETG to this product should increase minimum wall thickness or reduce local strain at bosses and living hinges. Conversely, when the design priority is dimensional accuracy across a print run, the homopolymer’s lower die swell and stable viscosity at 235–250 °C tends to produce more consistent bead width than PLA or PETG on open-frame printers.

The comparative table lists typical unfilled filament property ranges reported in supplier datasheets. Differences in specimen preparation, printing orientation, and moisture condition prevent direct substitution of these values into finite-element models without converter-specific validation.

Chemical contact data for the BASF Ultrafuse PET grade should be verified using ISO 175:2010 or ASTM D543 immersion protocols, particularly when the printed article is exposed to ketones, chlorinated solvents, concentrated alkalis, or acidic solutions above 40 °C. Polyethylene terephthalate homopolymer generally withstands dilute mineral acids, aliphatic hydrocarbons, and many alcohols at room temperature, but stress cracking can occur in aromatic solvents and strong caustic environments. For food-contact printed parts, converter validation is required because the filament’s raw-material compliance does not automatically extend to the final layer-porous surface. Relevant regulatory frameworks include FDA 21 CFR 177.1630 for PET homopolymers and Regulation (EU) No 10/2011 for plastic food-contact materials; migration testing and cleaning validation must account for layer lines, internal voids, and printer-specific contaminants.

In comparison with ABS, BASF Ultrafuse PET does not generate styrene monomer odour and has better resistance to oils and many weathering agents, but its dry-bed requirement and lower notched impact place it closer to PLA in toughness. Operators should not select this filament for high-speed tooling parts that require service above 80 °C or repetitive impact loading. For such conditions, polycarbonate, ASA, fibre-filled polyamide, or impact-modified copolyester grades may be required depending on the thermal and mechanical demand.