UV aging of 3D printing materials

Of the four 3D printing materials compared here, ASA is the only one designed for permanent UV and weathering exposure outdoors; PLA and standard PETG are unsuitable for it. Under short-term UV-C irradiation the ranking of the latter two is reversed: after 24 hours at 254 nm, PETG loses 38 % of its tensile strength, PLA only 9 % [1]. “Resistant to sunlight” and “resistant to UV-C” are therefore not interchangeable properties.

3D-printed plastic parts used outdoors or under UV irradiation change over time: they may fade, become brittle or lose strength. The cause is high-energy ultraviolet (UV) radiation, which can break chemical bonds in the polymer – a process known as photo-oxidative aging. Three ranges are broadly distinguished:

• UV-A (315–400 nm): the largest share of the sun’s UV light, responsible for slow aging over months and years.
• UV-B (280–315 nm): the more energetic share of sunlight, accelerating aging further.
• UV-C (200–280 nm): barely reaches the earth’s surface in nature, but is used deliberately in disinfection equipment because it inactivates microorganisms particularly effectively – and, for the same reason, can attack plastics particularly strongly [8].

But how stable are common 3D printing materials – PLA, TPU, PETG and ASA – against UV light and UV-C radiation? The following overview summarises what can be supported by measured data and where the evidence remains thin.

The spectral ranges themselves are covered in detail by What is UV radiation?, the aging mechanisms in materials by UV aging, color fastness and photostability. Measurement technology for the printing and post-curing process is covered by UV measurement for additive manufacturing and 3D printing.

The studies cited describe UV damage in terms of three mechanical quantities. Each of them says something different:

• Tensile strength: the force per unit area a part withstands before it tears. A drop in tensile strength after UV exposure means the material has become weaker.
• Elongation at break: how far a material can be stretched before it breaks. A falling elongation at break indicates that a material is becoming more brittle.
• Embrittlement: the polymer loses its elasticity and breaks more easily – often a visible early sign of UV damage.

Of the four materials compared, ASA is best suited to permanent UV and weathering exposure; PLA and standard PETG are unsuitable for it. One central finding runs counter to the usual expectation: under controlled UV-C irradiation over 24 hours, PETG loses considerably more strength (−38 %) than PLA (−9 %) [1]. This shows that “good in sunlight” does not automatically mean “good under UV-C” – the two types of radiation act differently on the same polymer.

The following table places the behavior under natural weathering alongside the behavior under UV-C irradiation. The UV-C values for PLA and PETG come from the same test series and are therefore directly comparable; for TPU and ASA, measurements of comparable methodology are missing.

PLA is the entry-level material in 3D printing: inexpensive and easy to print, but sensitive to heat and UV light.

• Generally not UV-stable: embrittlement and discoloration with prolonged outdoor use [2].
• Under UV-C (24 h, 10 W/m², 254 nm): no visible changes, tensile strength −9.1 % (29.54 to 26.86 MPa), compressive strength −13.1 %, Young’s modulus practically unchanged (−1.9 %, not statistically significant) [1].
• Conclusion: short-term UV-C exposure is tolerated comparatively well in mechanical terms, permanent outdoor weathering is not.

TPU is a rubber-like, flexible material that can be bent and stretched – for seals or grips, for example.

• Standard TPU is not UV-stable [3].
• With UV additives – fillers such as titanium dioxide or zinc oxide that absorb UV light – UV resistance and the retention of tensile strength and elongation at break after UV aging improve markedly; the source does not give specific figures [3].
• No reliable UV-C-specific data available.

PETG is tougher and more impact-resistant than PLA and is therefore often used for functional parts.

• Better weathering resistance than PLA, but not designed for permanent UV exposure; can turn rubbery and soft under continuous sunlight [4].
• Under UV-C (conditions identical to PLA): considerably more damage than PLA – tensile strength −38.1 % (31.30 to 19.48 MPa), compressive strength −33.9 %, elongation at break from 3.06 % to 1.36 % (severe embrittlement), visible yellowing and loss of gloss [1].
• Specially UV-stabilised PETG grades exist for outdoor applications (maximum continuous service temperature 70 °C), but they are not the same as standard PETG for 3D printing [5].

ASA was developed specifically for outdoor use and is regarded as the most weather-resistant of the printing materials compared here.

• Developed specifically for UV and weathering resistance: the UV-sensitive rubber component of ABS is replaced by a more UV-stable acrylic ester [2].
• Retains around 85 % of its tensile strength after 2,000 hours of UV irradiation in the laboratory test to ASTM G154 [6].
• 122-day outdoor test: no significant loss of properties under intense UV exposure [7].
• No quantified UV-C-specific measurements available. A laboratory statement of 100 h of direct UV-C irradiation without discernible change is plausible given the general UV robustness, but is not methodologically comparable with the PLA/PETG study.

The UV-C values for PLA and PETG come from a test series published in Polymers in 2021 [1]. The printed specimens were irradiated for 24 hours at 254 nm and 10 W/m², with a back panel temperature of 50 °C; the samples then cooled for four hours at room temperature before tensile and compression tests were carried out. The paper names the UV irradiation chamber BS-02 from Opsytec Dr. Gröbel as the irradiation equipment used.

Two points decide whether such values can be transferred to your own application. First, they refer to the measured irradiance at the sample position and the dose resulting from it, not to an equipment setting – without measurement, exposures are not comparable. Second, they apply to specimens with a defined layer thickness, orientation and infill; wall thickness, infill ratio and color pigmentation shift the result considerably. Anyone who has to demonstrate the UV resistance of a specific part therefore tests it in their own setup: UV irradiation chambers provide the reproducible boundary conditions, the relevant standards and guidelines the framework for the test conditions.

• Permanent outdoor use with high UV exposure: prefer ASA.
• Short or recurring UV-C disinfection cycles on the order of hours: in the only comparative study available, PLA shows smaller mechanical losses than standard PETG.
• ASA under UV-C: data of comparable methodology to PLA and PETG are still missing here. For safety-relevant parts, testing them yourself is advisable, for example in a UV-C irradiation chamber.
• TPU: use for outdoor and UV applications only with UV-stabilising additives.

Parts that are not printed but bonded or potted are subject to their own boundary conditions; these are covered by UV-curing adhesives, coatings and potting compounds.

1. Amza CG, Zapciu A, Baciu F, Vasile MI, Popescu D: Aging of 3D Printed Polymers under Sterilizing UV-C Radiation. Polymers 13(24):4467, 2021.
2. Spectrum Filaments: ASA 275 Explained – The Right Filament for Outdoor Use.
3. Wang A, Guo J, Shao C, Chen C: Flexible Thermoplastic Polyurethane Composites with Ultraviolet Resistance for Fused Deposition Modeling 3D Printing. 3D Printing and Additive Manufacturing, 2024.
4. Makelab: PETG vs. ASA.
5. Noltewerk: PETG UV technical data sheet (PDF).
6. Forge Labs: ASA Material Properties.
7. Habr: 122-day comparative UV test on 3D printing materials.
8. Teska P (NIST): Damage to Common Healthcare Polymer Surfaces from UV-C Exposure (PDF).

Editorial status: 3 September 2026.

Whether a printed part survives the UV exposure of its place of use is only answered by a test with defined irradiation and a measured dose. We supply the measurement technology for it: UV irradiation chambers such as the BS-02 for reproducible aging tests in the laboratory, the UVpad spectroradiometer and the Radiometer RMD Pro for measuring spectrum, irradiance and dose at the part itself. Send us your question.