Heat resistance under load: HDT, Tg, annealing and service temperature

One grade, two stresses, two thermal states

Polymaker labels these HT-PLA results as printed or annealed. The sheet does not identify HDT-specific orientation, geometry, heating rate, conditioning or specimen count. Unknowns remain visible in each test record; the listed values are supplier typical results, not component design limits. Polymaker [details] · ISO [details]

Engineering interpretation. Read the stresses as separate tests. The annealed result at the lower stress cannot replace the higher-stress result when screening a loaded feature. Neither is a safe operating temperature for an arbitrary geometry. Polymaker [details] · Polymaker [details] · ISO [details]

Tg, HDT and Vicat measure different responses

Engineering interpretation. A DSC Tg comes from a heat-capacity change. A DMA Tg is assigned from a change in viscoelastic response; the technique and its frequency matter. Ask which definition was used, and retain the scan rate, thermal history and conditioning when reported. Do not treat a Tg entry as a load-bearing endurance result. ASTM International [details] · ASTM International [details]

Engineering interpretation. HDT observes deflection while a loaded specimen is heated. ISO 75-2 distinguishes a 0.45 MPa stress from a 1.8 MPa stress. Vicat instead observes needle penetration. A higher Vicat value does not supply the missing HDT value for a housing wall or fixture arm. ISO [details] · ASTM International [details]

Keep ASTM D648 results outside an ISO 75 numerical comparison. The ASTM scope explicitly distinguishes their technical content. Matching the word “HDT” or rounding their stress labels does not make the methods interchangeable. ASTM International [details]

Treat annealing as a manufacturing state to qualify

Independent work by Benwood and colleagues on True Red PolyLite PLA supports a mechanism: the printing and post-print thermal history changed crystallinity and the measured heat-deflection response. That study used its own FDM process and ASTM D648 procedure. Its results and annealing recipes are kept separate from the HT-PLA supplier table. ACS Omega [details]

Engineering interpretation. For an annealed candidate, qualify the complete sequence: printing, the actual part-temperature history, support during heating, cooling and final inspection. Check critical holes, locating surfaces and assembled fit after treatment. If the annealing schedule behind a published result is unknown, request it before treating a recommendation as a reproduced test condition. Polymaker [details] · ACS Omega [details]

Use the service load to choose the next measurement

Engineering interpretation. For a hot locating fixture, measure drift at the locating surface while it carries the required force. For an electronics housing, inspect loaded standoffs, latches and fasteners after the required thermal hold and cycles. For a tool touching a hot workpiece briefly, reproduce the contact duration and cooling cycle. These examples define component checks; they are not claims that the illustrated grade has passed them. ISO [details]

Long holds need time-dependent evidence. Fischbach and Weinberg observed continuing creep in a printed Ultrafuse PLA specimen below its glass transition during a room-temperature hold. This does not predict the HT-PLA grade’s life; it shows why being below Tg alone cannot establish dimensional stability under sustained load. Fischbach and Weinberg [details]

Engineering interpretation. If the candidate lacks appropriate creep or retained-property data, test a representative part at its service temperature and environment. Include the load path and attachment points. Define allowable drift and permanent set before the test; do not invent a universal temperature margin below HDT. ISO [details] · Fischbach and Weinberg [details]

What these records establish and what remains unknown

The supplier’s “as printed” thermal labels establish a printed-material basis, but its mechanical coupon drawings do not establish the HDT orientation. General specimen instructions are also not a confirmed HDT recipe. Annealing state is known where labeled; the exact thermal-test annealing schedule remains unknown. Polymaker [details]

A similar source-boundary issue appears in the Prusament PC Blend sheet: HDT is in its typical-material table, outside the separately labeled printed-mechanical table. This article does not assign those thermal values the tensile specimen’s orientation or printing recipe. Ask the supplier for the thermal specimen process before comparing that row with confirmed printed tests. Prusa Polymers a.s. [details]

The comparison still needs HDT specimen geometry, build orientation, heating rate, conditioning and replicate information, plus sustained-load or component evidence for the proposed use. A document access date records consultation, not a fresh test. Polymaker [details] · ISO [details]

Before selecting a hot fixture, housing or tool

Engineering interpretation. Use these as project checks, with acceptance limits chosen for the actual function. A thermal label alone cannot close them. ISO [details]

1. Record the exact grade and lot where relevant, fabrication process, orientation and full post-processing state. Preserve the measured part-temperature history if annealed.

2. Check the temperature at critical loaded features, including local heat sources and the required hold or contact cycle.

3. Verify displacement, permanent set and fit under the actual supports, fasteners and load; repeat the relevant thermal and moisture conditions.

4. Where endurance matters, obtain or generate time-dependent data over the required conditions. Recheck the geometry or manufacturing route if the evidence cannot support the required margin. ISO [details] · Fischbach and Weinberg [details]

Explore the candidate grades

Use the reference guides to find settings and individual product sources, then check the exact grade against the evidence above.

• PLA material guide
• PETG material guide
• ASA material guide
• PC material guide

Sources and evidence records

These records distinguish supplier tests, independent experiments and engineering interpretation. “Not reported” identifies a source gap; it is not an assumed test condition.

1. Prusament PC Blend technical data sheet

   Prusa Polymers a.s. · Manufacturer test · document date: 2022-02-16 · version: 1.1 · accessed 2026-10-18
   Prusa Polymers a.s.

   Manufacturer measurements on FFF coupons for this commercial product; color, lot and reinforcement content are not specified. No raw replicate data or definition of the reported plus/minus term is supplied. Printed-coupon tensile results do not report conditioning, test temperature, test rate, detailed dimensions or specimen count. The 24 °C / 22% humidity footnote belongs to the separate moisture-uptake rows and is not treated as a tensile conditioning protocol. Its polymer is described as a PC blend; the other blend constituents are not identified.

2. Effect of physical aging on the flexural creep in 3D printed thermoplastic

   Fischbach and Weinberg · Independent experiment · document date: 2023-08-16 · version: arXiv:2302.11240v2 · accessed 2026-10-18
   Marcel Fischbach, Kerstin Weinberg

   Author manuscript, printed BASF Ultrafuse PLA; 100% infill, 0.2 mm layers, 215 °C nozzle, 30 °C bed; ISO 899-2 bending creep. The long-duration test uses one specimen under a 10 N nominal force for 170 h near 20 °C. No family-wide lifetime or reduction factor is inferred. The long-duration specimen had an initial age of five hours; the authors report laboratory relative humidity of 30–50%.

3. ISO 75-1:2020 — Plastics — Determination of temperature of deflection under load — Part 1: General test method

   ISO · Test method scope · document date: 2020-02-28 · version: ISO 75-1:2020, edition 4 · accessed 2026-10-18
   ISO

   Public abstract, not the paid full standard. Its method scope and limits explain HDT; it does not establish the edition used by the filament supplier.

4. ISO 75-2:2013 — Plastics — Determination of temperature of deflection under load — Part 2: Plastics and ebonite

   ISO · Test method scope · document date: Not reported · version: ISO 75-2:2013, edition 3; publication month 2013-04 · accessed 2026-10-18
   ISO

   Public abstract identifies the method stresses. Exact publication day was not recorded; no day is invented.

5. ASTM D648-18 — Standard Test Method for Deflection Temperature of Plastics Under Flexural Load in the Edgewise Position

   ASTM International · Test method scope · document date: 2018-04-23 · version: D648-18 · accessed 2026-10-18
   ASTM International

   Public scope and significance/use explain the limits of this test and its technical differences from ISO 75. This does not certify supplier compliance.

6. ASTM D1525-25 — Standard Test Method for Vicat Softening Temperature of Plastics

   ASTM International · Test method scope · document date: 2025-03-04 · version: D1525-25 · accessed 2026-10-18
   ASTM International

   Public scope identifies the controlled needle-penetration measurement. No full standard text or product-specific Vicat qualification is reproduced.

7. ASTM E1356-25 — Standard Test Method for Assignment of the Glass Transition Temperatures by Differential Scanning Calorimetry

   ASTM International · Test method scope · document date: 2025-01-22 · version: E1356-25 · accessed 2026-10-18
   ASTM International

   Public scope and significance/use explain the DSC heat-capacity transition, rather than a component load-bearing limit.

8. ASTM E1640-23 — Standard Test Method for Assignment of the Glass Transition Temperature By Dynamic Mechanical Analysis

   ASTM International · Test method scope · document date: 2023-08-15 · version: E1640-23 · accessed 2026-10-18
   ASTM International

   Public significance/use explains the viscoelastic transition, dependence on the measurement technique, and the ideal storage-modulus-onset interpretation.

9. Polymaker HT-PLA Technical Data Sheet

   Polymaker · Manufacturer test · document date: Not reported · version: V1.1 in the linked PDF filename; no printed issue date identified · accessed 2026-10-18
   Polymaker

   PDF thermal rows explicitly separate as-printed and annealed material. HDT geometry, orientation, conditioning, replicate count, heating rate and actual annealing schedule are not identified. The general specimen recipe and recommended anneal are not silently assigned to the HDT tests.

10. Improving the Impact Strength and Heat Resistance of 3D Printed Models: Structure, Property, and Processing Correlationships during Fused Deposition Modeling (FDM) of Poly(Lactic Acid)

    ACS Omega · Independent experiment · document date: 2018-04-23 · version: ACS Omega 3(4), 4400–4411; DOI 10.1021/acsomega.8b00129 · accessed 2026-10-18
    Claire Benwood, Andrew Anstey, Jacek Andrzejewski, Manjusri Misra, Amar K. Mohanty

    True Red PolyLite PLA, 2.85 mm filament, Lulzbot Taz 6. The study combines printed and separately identified injection-molded specimens; only its printed-process observations inform this article. Its ASTM D648 experiment is kept separate from supplier ISO 75 results.