The spec, the moisture story, the honest limits, and where PETG actually wins · cross-checked against the manufacturer's TDS V5.4, written by the team that prints it.
Custom PETG 3D printing service · UK · quoted in 6 hours.
Stronger than PLA, easier to print than ABS, and happy around water · no chamber needed.
Four quick visuals. Start with which material to pick and where PETG works; the engineering detail is at the end if you want it.
A fraction of the ethylene glycol monomer is replaced with cyclohexanedimethanol (CHDM), which breaks the crystal symmetry. The result: same PET chemistry, no warping, food-bottle heritage.
PETG yields at 8.4% strain (33% more give than PLA's 6.3%). Notched Charpy is similar to PLA (2.6 vs 3.3 kJ/m²) · the real win is yield behaviour on impact. For raw toughness: ABS at 18.0 kJ/m² (7× higher) or PA12-CF for engineering-grade.
"James handled the 3D printing for a functional heat resistant component we needed in batch production. He helped dial in the prototype first with their design service, then produced the final batch with really consistent results. Super fast 3D print turnaround and great quality across all the 3D printed parts. Will 100% be coming back."
"We needed a sit-in F1-car for an exhibition to showcase our new racing game. 3D Printing Express took our CAD, optimised it for strength and weight as we had no idea how it all worked! Turned out beautifully. They colour matched the finish and was looking like the real deal. On show day the cockpit ran non-stop, adults and kids jumped in. Multiple visitors asked who built it."
"We ordered a batch of 100 PA-12 parts from 3D Printing Express and could not be happier. Every part arrived consistent, dimensionally accurate, and ready for use straight from the box. The PA-12 gave us the strength and stability we needed for functional testing, with minimal post-processing required. Delivery was on time, communication was excellent, and their QC clearly made a difference."
Effectively tied with PLA (52.3 MPa) on raw tensile · the real PETG advantage is ductility (8.4% elongation vs PLA's 6.3%) and better Z-axis strength.
18°C higher than PLA's 60°C cliff. Survives cold-to-warm water service and UK summer outdoor (months). Engine bay / autoclave is still wrong material.
Hygroscopic at equilibrium · we dry every spool at 65°C for 6 hours before printing per the manufacturer's setting. Wet PETG prints stringy, milky, brittle.
PETG earns its place when ductility, moisture tolerance, and moderate-temperature service matter · the commodity workhorse for water-contact, food-adjacent, and outdoor-moderate parts.
PETG's strengths are ductility, water resistance, and moderate-service breadth · its weaknesses are sustained heat above 70°C, ketone / strong-alkali exposure, multi-year outdoor UV, and impact-critical service. Pick a different filament if any of these apply.
Prototype the shape in PETG (same chemistry family as the production part), certify the final grade for production. Base PET is FDA 21 CFR 177.1630 compliant for food contact in moulded form · prototyping in PETG keeps the chemistry consistent.
PETG's hydrolytic stability and PET-backbone heritage make it the right material for cold-to-warm water service. Used in irrigation, fountain components, humidity-sensor housings, pump brackets, vases.
Moderate UV resistance and translucent grades make PETG the standard for FDM signage. 6-12 month outdoor service uncoated, multi-year with UV overcoat. translucent PETG variants specifically marketed for light-transmission display work.
PETG's ductility means impact loads bend or yield rather than snap clean. Machine guards around moving equipment, workshop splash guards, electronic enclosures where a dropped tool would crack PLA or fracture ABS.
A side-by-side of the three commodity thermoplastics most engineers compare when picking PETG. Each material wins on one axis · PLA on stiffness and cost, ABS on impact and heat, PETG on ductility and water-contact service. Pick PETG when you need the all-rounder.
All values from manufacturer Technical Data Sheets V5.4 EN · injection-moulded ISO test specimens (ISO 527 tensile + elongation, ISO 75 HDT, ISO 179 Charpy notched). The chart shows where each material wins · PETG's wedge is ductility plus water/food-contact heritage, not raw strength or heat.
| Property | PETG (here) | PLA | ABS / ASA |
|---|---|---|---|
| Tensile strength XY | 50.8 MPa | 52.3 MPa | 33.4 MPa |
| Stiffness (Young's modulus XY) | 2117 MPa | 3427 MPa | 2247 MPa |
| Charpy notched impact | 2.6 kJ/m² | 3.3 kJ/m² | 18.0 kJ/m² |
| Elongation at break XY | 8.4% | 6.3% | 17.9% |
| Heat deflection (HDT 0.45) | 78°C | 60°C | 100°C |
| Glass transition (Tg) | 81°C | 61°C | 101°C |
| Density | 1.25 g/cm³ | 1.17 g/cm³ | 1.04 g/cm³ |
| Water-contact service | Yes · PET-backbone hydrolytic stability | Limited · slow hydrolysis | Yes · low water absorption |
| Food-contact base chemistry | FDA 21 CFR 177.1630 compliant (base polymer) | Not certified | Not certified |
| Outdoor / UV (years) | 6-12 months uncoated | Months only | ASA grade: 5+ years |
| Print difficulty | Moderate · drying required | Easiest | Hardest · chamber needed |
| Cost per kg (filament) | £25-40 | £20-35 | £30-45 |
| Best for | Water-contact, food-adjacent prototypes, signage, ductile enclosures | Visual prototypes, props, indoor cosmetic | Heat / outdoor (ASA) / impact-loaded parts |
This is 3DPE's standard process for PETG · the equipment and the dried-filament discipline are included, no surcharge. Slicer profile and orientation are tuned per part at quote stage.
File or sketch in. Tell us colour, finish, water / food-adjacent or structural use.
Reviewed inside 24 hours · per-unit cost + colour confirmation.
Wall thickness, overhang, support strategy, ductility-vs-load fit flagged before print.
Filament dried at 65°C for 6 hours (mandatory for PETG) · calibrated machine · stock or custom-RAL colour matched.
Sand to spec · 2K spray paint if needed · food-safe epoxy overcoat where requested.
Tracked UK courier, tracking number sent the moment it leaves.
Lead times start when CAD is signed off and colour is confirmed · CAD round-trips on rev requests can extend the clock. Custom RAL colour matching can add 1-2 days for filament procurement. Food-safe epoxy overcoat adds 24h for cure.
Production batch of water-contact irrigation fittings printed in standard PETG · stock-colour translucent grade, cosmetic-quality glossy finish out of process. PET-backbone hydrolytic stability proven in cold-to-warm water service. Indoor / outdoor commercial-grade use case · the part profile PETG was designed for.
PETG is polyethylene terephthalate, glycol-modified · an amorphous copolyester where a fraction of the ethylene glycol monomer is replaced with cyclohexanedimethanol (CHDM). The base PET polymer is the same chemistry used in plastic water bottles, food packaging, and polyester fibre; the CHDM modification breaks the crystal symmetry and lets PETG print on FDM without the warping problems of crystalline PET. Tensile strength 50.8 MPa XY (ISO 527), HDT 78°C at 0.45 MPa (ISO 75), Young's modulus 2117 MPa, elongation at break 8.4% (more ductile than PLA's 6.3%). Density 1.25 g/cm³. The base polymer is FDA 21 CFR 177.1630 compliant for food contact in moulded/extruded form · the printed grade is not certified, but the chemistry makes certification straightforward.
"PETG is the material I reach for when the brief includes water, food-adjacent service, or mild outdoor exposure · or when the customer dropped a PLA prototype and watched it snap. It's the ductile commodity that does most of what people think PLA does, plus a meaningful jump in heat tolerance (78°C vs 60°C HDT) and the PET-backbone water story. The two catches are mandatory pre-print drying (PETG is hygroscopic · we condition every spool at 65°C for 6 hours) and the moderate UV ceiling. For multi-year outdoor we still recommend ASA."
Three questions worth answering before specifying PETG · where the polymer comes from, why it's hygroscopic, and where the 75°C HDT cliff really matters.
Base PET is the most-produced thermoplastic on Earth · food bottles, packaging, polyester fibre. Glycol modification (CHDM replaces some ethylene glycol) breaks the crystal symmetry, prevents crystallisation, and makes PET 3D-printable on FDM without the warping of crystalline PET.
PETG absorbs water from humid air, saturating at ~0.54% per the manufacturer TDS. Wet PETG prints stringy, milky, brittle. The fix is straightforward · pre-print drying at 65°C for 6 hours (manufacturer setting). We do this on every spool before the bed.
PETG is polyethylene terephthalate, glycol-modified · an amorphous copolyester. The base PET chemistry is the same polymer used in plastic water bottles, polyester clothing, and most food packaging. The modification: a fraction of the ethylene glycol monomer in the backbone is replaced with cyclohexanedimethanol (CHDM). That substitution breaks the crystal symmetry of the backbone and prevents the polymer from crystallising.
The chemical formula shifts from PET's -[O-CH₂-CH₂-O-CO-C₆H₄-CO]-n to PETG, where some of the -CH₂-CH₂- ethylene-glycol units are replaced with the larger -CH₂-C₆H₁₀-CH₂- CHDM rings. The result is a glass-clear, amorphous thermoplastic that prints beautifully on FDM without the warping problems of crystalline PET. This matters for three reasons: amorphous structure means no crystallisation shrinkage on cooling (large flat parts stay flat); PET backbone heritage gives PETG real chemical and moisture resistance; and the food-contact compliance of base PET (FDA 21 CFR 177.1630) carries through the chemistry for certified food-grade variants.
PETG absorbs moisture from humid air · equilibrium water absorption is 0.54% per the manufacturer TDS, reached over days to weeks in 60% RH workshop conditions. The hydroxyl groups introduced by the glycol modification are mildly polar, which is why PETG holds onto water more than purely non-polar polymers like polyethylene.
Wet PETG prints badly. Water in the filament flashes to steam at the nozzle (which sits well above water's boiling point), producing visible stringing, milky surface finish, and reduced layer adhesion. The brittleness of wet-printed PETG parts is the most common reason for "PETG broke at the layer line" complaints. The fix is straightforward · pre-print drying at 65°C for 6 hours (per the manufacturer's recommended setting) and storing the spool in a sealed dry-box with desiccant. We run every PETG spool through a filament drier before the bed; a maker skipping this step gets noticeably worse parts.
PETG's glass transition temperature (Tg) sits at 81°C (DSC, 10°C/min). Below Tg the polymer chains are locked in the amorphous network and the part holds its shape. Above Tg the chains gain mobility · stiffness collapses, the part softens, and any residual stress from printing relaxes into creep. Heat deflection temperature (HDT) at 0.45 MPa load is 78°C, dropping to 75°C at 1.8 MPa load. Vicat softening at 84°C. For sustained service the practical ceiling is ~70°C · a PETG part in a car dashboard in summer, near an engine, or pressed against a radiator will creep and deform.
Steam autoclave at 121°C is well above HDT · parts deform. For sterilisation, ethylene oxide or IPA wipe-down work for PETG; dry-heat sterilisation below 70°C also works. For repeated steam autoclave service specify PEEK or PPSU. For sustained warm-service parts (engine bay, exhaust-adjacent, oven-adjacent) choose ABS or ASA (HDT 100°C class) or PA12-CF (HDT 130°C+ class).
Values measured to the ISO standards cited in the right-hand column, on the manufacturer's own injection-moulded test specimens · directly comparable to other engineering thermoplastics.
| Property | XY · print plane | Z · build axis | Unit | Standard |
|---|---|---|---|---|
| Mechanical | ||||
| Tensile strength | 50.8 | 42.8 | MPa | ISO 527 |
| Young's modulus | 2117 | 1899 | MPa | ISO 527 |
| Elongation at break | 8.4 | 3.3 | % | ISO 527 |
| Flexural strength (XY) | 69.6 | MPa | ISO 178 | |
| Flexural modulus (XY) | 1899 | MPa | ISO 178 | |
| Charpy impact (notched, XY) | 2.6 | kJ/m² | ISO 179 | |
| Thermal | ||||
| Heat deflection (HDT @ 0.45 MPa) | 78 | °C | ISO 75 | |
| Heat deflection (HDT @ 1.8 MPa) | 75 | °C | ISO 75 | |
| Glass transition temperature (Tg) | 81 | °C | DSC, 10°C/min | |
| Vicat softening temperature | 84 | °C | ISO 306 | |
| Physical | ||||
| Density | 1.25 | g/cm³ @ 23°C | ISO 1183 | |
| Equilibrium water absorption | 0.54 | % | manufacturer test | |
| Melt index | 10.8 | g/10min | 240°C, 2.16kg | |
| Light transmission | 90 | % | GB/T 2410 | |
| Tensile anisotropy ratio | 1.19× | XY/Z | derived from ISO 527 | |
| Chemical resistance · manufacturer-rated | ||||
| Weak acids | Good | · | manufacturer TDS | |
| Strong acids | Poor | · | manufacturer TDS | |
| Weak alkalis | Fair | · | manufacturer TDS | |
| Strong alkalis | Poor | · | manufacturer TDS | |
| Oils and grease | Good | · | manufacturer TDS | |
| Cosmetic / supply | ||||
| Stock colour range | 20+ colours (incl. translucent + clear grades) | · | workshop stock | |
| Custom RAL match | Yes (1-2 day procurement) | · | on request | |
| Finish grades available | Glossy as-printed, sanded, painted, translucent | · | workshop stock | |
| Food-contact base polymer | PET base · FDA 21 CFR 177.1630 compliant (printed grade NOT certified) | · | FDA regulation | |
PETG's anisotropy is mild (1.19× XY/Z · 50.8/42.8 MPa per TDS V5.4) · actually slightly less anisotropic than PLA (1.29×). For visual prototypes orient for cosmetic finish (best surface upward). For load-bearing PETG parts, still favour XY-direction load paths.
PETG's higher elongation (8.4%) means thin walls handle impact better than PLA's, but layer-line geometry still dominates. The values shown follow the Hubs / Protolabs Network FDM minimums (0.8 mm supported, 2.0 mm minimum feature) · we DFM-check the wall thickness against your part's load case at quote stage.
45° is the slicer-default support threshold across every major FDM tool · PETG's slower cooling and stickier hot state typically holds long bridges (5 mm+ at print temperature) better than PLA. Exact threshold depends on cooling, geometry, and surface-finish tolerance · we DFM-check overhangs at quote stage and recommend orientation.
PETG's amorphous structure means no crystallisation shrinkage on cooling (good) but the lower stiffness means slightly more deflection during finishing (modest). Exact tolerance depends on part size, geometry, and calibration · we confirm achievable tolerance against your CAD at quote stage.
Removes 0.1-0.3 mm per surface · pre-paint prep or stand-alone hand-feel polish.
Wet PETG (the spool has been in humid air more than ~3 days) prints stringy, milky, and brittle. Pre-print drying is per the manufacturer's recommended setting · we run this on every spool before the bed.
PETG takes paint with adhesion-promoting primer (PETG resists direct paint adhesion more than PLA). Adds 0.05-0.15 mm per surface · sand to 800 grit, primer + topcoat · paint also acts as a UV barrier for outdoor service.
The real food-contact risk on FDM PETG isn't the polymer · it's bacteria in micro-gaps between layers. A food-safe epoxy overcoat (we use NSF-certified two-part) bridges the layer-line porosity and gives a continuous food-adjacent surface. Adds 0.05-0.1 mm per surface and 24 hours cure.
Every value on this page traces to an ISO test method · the manufacturer's V5.4 EN TDS, cross-checked against the PDF in-session. We don't quote derived numbers without naming the standard.
No offshore subcontracting. Files, prints, and couriers all stay in the UK · and we dry every PETG spool at 65°C for 6 hours before the bed, per the manufacturer's recommended setting.
Send three things: where the part lives (water, food-adjacent, outdoor, indoor), what it does (cosmetic / functional / load-bearing), and colour / finish. our team come back inside 24 hours · if PLA, ABS, ASA, or another material fits better, we say so.
our team review every brief before quote. No ticket queue, no account managers.
According to the PolyLite PETG TDS, PETG delivers tensile XY 50.8 ± 0.9 MPa per ISO 527 with HDT 78 °C @ 0.45 MPa and Tg 81 °C · fully amorphous, no crystalline melt.
We print PETG at 230–260°C nozzle and 70–80°C bed, open frame with light part cooling, on a standard brass nozzle. PETG must be dried at 65°C for 6h before printing or you get bubbling and weak layers. The main print challenge is stringing and ooze, so we tune retraction, travel speed and temperature per part rather than running one generic profile. Bed adhesion is strong, so a release agent or textured plate is used to avoid tearing the sheet on removal.
Yes. We run a closed loop in our own workshop. Failed prints, purge, and support waste are collected, reground, and reprocessed here instead of going to landfill. That is standard on every PETG job, no surcharge.
Tensile strength XY is effectively a tie · 50.8 MPa PETG vs 52.3 MPa PLA (per TDS V5.4 for both). PLA wins on stiffness (Young's modulus 3427 vs 2117 MPa · 62% stiffer). The real PETG advantage is ductility · elongation at break 8.4% vs PLA's 6.3% (33% more strain before failure). PETG bends and yields under impact where PLA snaps clean. Notched Charpy is similar (2.6 vs 3.3 kJ/m²). For raw impact toughness ABS still wins (18.0 kJ/m² Charpy notched · 7× higher than PETG).
The base PET polymer is FDA 21 CFR 177.1630 compliant for food contact in moulded and extruded form. Standard standard PETG is NOT certified for food contact · the certification applies to specific food-grade PETG variants, not to commodity FDM filaments. For a food-contact application 3DPE specifies a certified food-grade PETG variant and recommends a food-safe epoxy overcoat to seal FDM layer porosity (the real risk · bacteria can harbour in micro-gaps between print layers even when the polymer itself is food-safe). The honest answer: PETG is the right chemistry, but printed parts need certification + sealing for true food-contact service.
Genuinely yes for cold-to-warm water service. PETG has good hydrolytic stability and the base PET backbone is the same chemistry used in plastic water bottles. Suitable for hydroponic fittings, splash enclosures, water-tank brackets, and vases. Long-term sustained service above 60°C in hot water starts to degrade the polymer; for repeatable hot-water service specify PP or PEEK. Note: PETG itself absorbs moisture from humid air (0.54% equilibrium per TDS) · this affects print quality, not the waterproof-ness of a finished, dried part.
Moderate UV resistance · better than PLA, slightly better than ABS, not as good as ASA. The PET aromatic ring absorbs UV more stably than the aliphatic PLA backbone, which is why PET water bottles survive outdoor warehousing. For 6 to 12 months UK outdoor service uncoated PETG holds up reasonably (colour fade and surface micro-cracking begin around year 2). For multi-year outdoor service specify ASA or UV-stabilised PC. We use the phrase "moderate UV resistance" not "UV resistant".
Per the manufacturer TDS · GOOD against weak acids and oils/grease, POOR against strong acids and strong alkalis, FAIR against weak alkalis. Also dissolves partially in acetone and other ketones. For sustained chemical-service parts use PA12 or PP. Match your specific exposure below.
| Chemical / family | Resistance | Notes |
|---|---|---|
| Weak acids (acetic, citric, dilute organic) | Good | Manufacturer TDS rating · short-term storage |
| Strong acids (sulphuric, HCl, nitric) | Poor | Manufacturer TDS rating · polymer chain breakdown |
| Weak alkalis (dilute soap, mild bleach) | Fair | Manufacturer TDS rating · short-term only |
| Strong alkalis (caustic soda, ammonia) | Poor | Manufacturer TDS rating · ester bond hydrolysis |
| Oils and grease | Good | Manufacturer TDS rating · sustained contact OK |
| Cold water, sea water (cold) | Excellent | PET-backbone hydrolytic stability · proven in bottles |
| Hot water (sustained > 60°C) | Limited | Approaches HDT · hydrolysis accelerates over months |
| Steam autoclave (121°C) | Fails | Above HDT · parts deform · choose PEEK / PPSU |
| Detergents, soap (mild) | Good | Dishwasher-style detergents · short-cycle only (heat above 60°C is the limit) |
| Alcohols (IPA, ethanol, methanol) wipe | Good | Surface cleaning, no soak |
| Acetone, MEK (ketones) | Poor | Partial dissolution · industrial degreaser, nail polish remover |
| Toluene, xylene (aromatic hydrocarbons) | Poor | Degrades over time |
| Petrol, diesel (brief contact) | Limited | Brief OK · sustained attacks the polymer |
| Chlorinated solvents (DCM, chloroform) | Poor | Strong solvents · industrial use only, workshop hazards |
| Swimming pool chemistry (chlorine, bromine) | Limited | Short-term OK · sustained immersion attacks the polymer |
| UV exposure (UK outdoor) | Limited | 6-12 months uncoated · multi-year requires overcoat or ASA |
| Outdoor weathering (sheltered) | Good | Rain-tight under cover, hydroponic outdoor, garden irrigation |
| Food contact (base PET chemistry) | Excellent | FDA 21 CFR 177.1630 compliant base · printed grade needs certification + sealing for true food-contact |
First five rows are direct manufacturer TDS ratings. Remaining rows reflect industry-typical PETG behaviour and 3DPE workshop experience · brief contact is always more forgiving than sustained exposure. For sustained chemical service beyond water and oils, switch material to ABS, PA12, or PP depending on the exposure.
Much less than ABS, slightly more than PLA. PETG is amorphous · no crystallisation shrinkage on cooling. Bed adhesion on PC, textured PEI, or buildtak is generally good. Large flat PETG parts stay flat. The biggest print issue is wet filament producing stringing and brittle layer adhesion, not warping · this is why we dry every spool at 65°C for 6 hours before printing per the manufacturer's recommended drying setting.
PETG is hygroscopic · equilibrium water absorption is 0.54% (per TDS) and the filament approaches saturation over days to weeks in humid UK workshop air. Water in the filament flashes to steam at the nozzle, producing visible stringing, milky surface, and reduced layer adhesion. Pre-print drying at 65°C for 6 hours (manufacturer setting) is mandatory for production work. A DIY maker skipping this step produces noticeably worse parts; we run every spool through a drier before the bed.
Different tools. PETG wins on: ease of print (no chamber needed, low VOC), water and food-adjacent service, moderate UV. ABS wins on: heat (HDT 98°C vs PETG 75°C), impact (Charpy 18.0 vs 2.6 kJ/m² · 7× tougher), acetone-smoothability for finishing, lower density (1.04 vs 1.25 g/cm³ · 17% lighter parts). If the part sees impact loads or sustained heat above 60°C, choose ABS. If it sees water, mild outdoor, or food-adjacent service, choose PETG.
Not with common solvents. PETG resists most chemistry that would bond it (acetone partially dissolves but doesn't cleanly fuse like it does for ABS). Use 2-part epoxy for structural bonds · cyanoacrylate works but bonds are weaker than on PLA or ABS. Ultrasonic welding works well. For multi-part assemblies, mechanical fasteners with heat-set inserts (245°C iron temp) are the most reliable joint.
No. Steam autoclave at 121°C is above PETG's HDT (75°C at 1.8 MPa) · parts deform. Dry-heat sterilisation below 70°C, ethylene oxide, and IPA wipe-down all work for PETG. For repeated steam-autoclave service (medical, dental, lab equipment) specify PEEK or PPSU.
Tg sits at 81°C · above this PETG softens. HDT is 78°C at 0.45 MPa and 75°C at 1.8 MPa (per TDS). Vicat softening at 84°C. A PETG part in sustained service above 70°C will creep and slowly deform. PETG handles 60°C hot water short-term, won't survive an engine bay, and is the wrong material for anything near a radiator or in direct summer sun on a hot surface. For warm-service parts choose ABS or ASA (HDT 100°C class).
Filament cost is roughly £25-40/kg for stock-colour PETG · slightly above PLA (£20-35/kg), below ABS (£30-45/kg), well below PA12-CF (£90-130/kg). The total quote depends on print time + post-processing more than filament cost · for a typical bracket or enclosure, material is 10-20% of the unit cost. Send the brief and we'll quote the actual job.
You'll hear back from our team within 24 hours · with material-fit check, colour confirmation, drying/lead-time confirmation, and food-safe overcoat recommendation if relevant.