Clear PETG is the most printable transparent filament for FDM. It’s not glass. It’s not acrylic. But with the right settings and some post-processing, it’s useful for light pipes, translucent covers, display windows, and anything where letting light through is the point. This guide covers what’s realistic and how to get there.
Set realistic expectations before starting.
Off the printer, clear PETG looks translucent rather than transparent. Layer lines scatter light internally, creating a frosted or hazy appearance. You can tell it’s not opaque, but you cannot see through it clearly at standard settings. Think frosted glass, not window glass.
With specific settings optimised for clarity, a well-tuned clear PETG print is noticeably more transparent. You can see shapes and light through it, but it still has a slightly milky quality compared to injection-moulded clear plastic.
With sanding and polishing, clarity improves significantly. A print sanded to 2000-grit and finished with a clear coat or polishing compound approaches the transparency of acrylic. It takes time, but the result is genuinely good.
For applications where optical clarity is critical — magnifying lenses, camera filters, precision light optics — FDM printing is not the right process. For light diffusion, decorative transparency, and parts where the material being see-through is a feature rather than a precision requirement, clear PETG works well.
Transparency in FDM printing is limited by three things that are all difficult to eliminate entirely.
Layer lines scatter light. Each layer boundary is a slight surface discontinuity. Light hits these boundaries and scatters in multiple directions rather than passing straight through. The finer the layer height, the less pronounced each boundary is, but even at 0.05mm the cumulative effect of many layers makes the part appear hazy.
Infill creates internal interfaces. Every infill line is an air gap or a polymer-to-polymer interface. Both scatter light. High infill percentage reduces air gaps but increases polymer interfaces. Rectilinear infill at 100% is the standard approach for clear PETG because it eliminates air gaps, but the infill lines are still visible.
Moisture in the filament causes bubbles. PETG is hygroscopic. Wet clear PETG produces microscopic bubbles throughout the print. Those bubbles are white and visible, making the part look milky regardless of settings. Dry filament before printing clear PETG. This is more important with clear PETG than with any other colour because the bubbles are immediately obvious.
The settings for clear PETG are deliberately different from standard PETG optimised for strength and surface quality.
Nozzle: 240-250°C. Higher temperature improves melt flow and reduces the visibility of layer interfaces by bonding layers more completely. The melt at higher temperature fills micro-gaps between layers better than a cooler, more viscous extrusion.
Bed: 70-85°C. Same as standard PETG.
Layer height: 0.20-0.30mm. Counter-intuitive, but thicker layers produce better clarity off the printer than thin layers for two reasons. Fewer layer boundaries means fewer scattering interfaces. Each thicker layer also bonds more thoroughly with the layer below it, reducing the refractive index difference at the interface. For post-processing to polished finish, thin layers are better because they have less surface relief to sand through.
Infill: 100% rectilinear. No air gaps. The rectilinear pattern aligns infill lines in one direction per layer, which produces more consistent light transmission than grid or gyroid patterns.
Perimeter count: 3-4. Extra perimeters reduce the visual disruption at the outer surface.
Cooling: off or minimal. More cooling increases layer boundary visibility. Reduce or disable the cooling fan for the best clarity at the cost of slight overhang quality.
Speed: 30-40mm/s. Slower than standard PETG. Slow speeds improve layer adhesion and reduce the micro-gaps that scatter light.
Post-processing makes a bigger difference to clarity than any settings change. The settings get you a good base. Post-processing takes it the rest of the way.
Wet sanding: start at 400-grit wet-dry sandpaper with water. Work through 800, 1200, 1500, 2000, and 2500-grit progressively. Each stage removes the scratches left by the previous grit. The surface becomes increasingly smooth and transparent as you progress. At 2000-grit, clear PETG is noticeably more transparent than off the printer. At 2500-grit it approaches the clarity of frosted acrylic.
Polishing compound: after 2500-grit, apply automotive plastic polishing compound with a soft cloth. Work in small circular motions. This removes the fine scratches left by the final sanding stage and brings the surface to a near-optical quality. Meguiar’s PlastX and similar products work well.
Clear coat: a spray coat of clear gloss varnish or UV-resistant clear coat after polishing seals the surface and improves transparency further by filling microscopic surface irregularities. Apply in thin coats and allow full cure between coats.
Flame polishing: a brief pass of a butane torch flame over the surface melts the very outermost layer, which then resolidifies as a smooth, glassy surface. This works well on flat surfaces and gentle curves but is difficult to control on complex geometry. Test on scrap first. It takes practice and the results are inconsistent until you’ve developed a feel for the dwell time.
Wall thickness affects clarity. Thin walls (1-2 perimeters) transmit more light than thick walls but are structurally weaker. For light pipe applications where maximum transmission is the goal, minimise wall count. For structural parts where clarity is a bonus, standard wall thickness is fine.
Orientation matters. Printing vertically (part standing upright) means light passes through fewer layer boundaries if the intended viewing direction is horizontal. Printing flat means more layer boundaries in the path of light. Think about how light will travel through the part when deciding orientation.
Avoid sharp internal corners. Sharp internal corners create stress concentrations and also scatter light more than radiused transitions. Fillet internal corners in the design for both structural and optical reasons.
Supports leave marks. Support contact points on clear PETG are very visible because the surface discontinuity scatters light. Design to minimise or eliminate supports on surfaces where clarity matters.
Light pipes and light guides: channelling LED light from a source to an indicator point on an enclosure. Clear PETG works well here because the internal reflections that scatter light for direct viewing actually help distribute light through a light pipe. Good for custom electronics enclosures, indicator panels, and illuminated props.
Translucent display windows: covers for display cases, sight glasses, and inspection windows on enclosures where you want to see inside without full exposure. The frosted quality of clear PETG without post-processing works well for this — it diffuses light while still showing forms and movement behind it.
Resin casting moulds: clear PETG makes good moulds for UV resin casting because you can see when the resin has filled the mould fully, and UV light can pass through the mould wall to cure the resin from the outside if needed.
Decorative translucent panels: backlighting a panel of clear PETG with LEDs produces an even, diffused glow that looks intentional. Thicker panels with high infill percentage diffuse the light more evenly than thin ones.
eSUN Clear PETG delivers consistent optical quality across spools. Consistency matters with clear PETG because batch variation in the base polymer affects the clarity of the finished print.
eSUN Clear PETG is available through the eSUN Official Store.
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