Transparent PC vs PETG: choosing by application

What the documents establish about transparency

Polymaker describes PolyLite PC as polycarbonate engineered for 3D printing with light-diffusing properties. Its table lists 89% transmission under GB/T 2410. That entry does not specify optical specimen thickness or preparation. It would therefore be incorrect to say this is a bulk-material measurement or, conversely, a measurement of your future printed cover. Keep the method, value and limitation together when reading another datasheet. A transmission figure without the matching preparation cannot establish how your particular housing will look.

Spectrum presents transparent PET-G Premium colors for semi-transparent housings and backlit sections of signs. The page describes a near-transparent effect with few outer perimeters, without a numerical transmission value in that description. This is a manufacturer statement for one product, rather than an optical ranking against PC. It does not convert perimeter count into a percentage of transmitted light or an ability to read through a finished cover. The linked 2022 PDF provides additional product information but no matching optical comparison.

Define your intended result before selecting a grade: recognizing a silhouette, reading a display behind a cover, or distributing light. These are suggested project criteria. The reviewed documents do not validate those three scenarios. For a visual trial, record thickness, geometry, profile, illumination and viewing distance. This editorial comparison is not a printing test performed by the site. It helps identify which checks remain necessary and which supplier statements cannot answer the question on their own.

Tg, Vicat and HDT: retain methods and limitations

The PolyLite PC sheet lists Tg at 113°C by DSC at 10°C/min, Vicat at 120°C under ISO 306/GB/T 1633, and two HDTs under ISO 75: 107°C at 1.8 MPa and 111°C at 0.45 MPa. These are separate properties. Its printed-specimen preparation includes 260°C extrusion, a 100°C bed, 100% infill and a 90°C environment. Do not transfer that preparation to the optical measurement when the optical entry does not establish it.

The Spectrum page lists Vicat at 78°C and HDT at 69°C. Its linked PDF, prepared on April 6, 2022, lists HDT at 70°C under ASTM D648 without a stated load here. The PDF does not resolve the page difference. Comparing PC Tg with PETG Vicat as though they were the same threshold would mislead. Even two entries named HDT require checking load, method and preparation before ranking them for a part. These documents do not establish a universal operating temperature.

Polymaker says its typical values are for reference and comparison, rather than design specifications or quality control. The Spectrum PDF makes the same distinction and mentions printing conditions, model complexity and environment. For a cover near a heat source, record the expected temperature, duration and load, then have the part's suitability evaluated. A datasheet number validates neither a lamp nor an enclosure window. The print-temperature guide separately covers manufacturing settings, which should not be confused with service limits.

PolyLite PC: read both the enclosure table and its note

Polymaker recommends a 250–270°C nozzle, a 90–105°C bed and cooling off. The enclosure table says “Needed (70–100°C).” Its note instead says an enclosure is recommended, with a heated chamber recommended for large parts. Preserve that wording difference. It does not justify declaring every open-frame printer incompatible here, or treating every passive enclosure as equivalent to a controlled heated chamber. If enclosure requirements determine your purchase, confirm the applicable guidance before making a compatibility conclusion.

The sheet lists textured PEI with glue when needed, 50–200 mm/s printing speed, and 1–3 mm retraction at 20–40 mm/s. These conditions are based on a 0.4 mm nozzle; the manufacturer says they may vary with nozzle diameter. They do not, on their own, constitute a validated profile for your printer. Also record its documented hotend, bed and environmental limits and the accessories actually installed before matching those ranges to equipment. A matching nozzle-temperature range alone does not settle the entire process.

Drying is listed at 75°C for six hours. Polymaker also recommends annealing at 90°C for two hours immediately after printing to release residual internal stress. That recommendation belongs to the documented PolyLite PC grade. It establishes neither a measured optical improvement nor a universal requirement for all transparent PC. The PC guide and enclosure page support preparation of a selection, while the applicable material profile and equipment limits still need checking for the actual setup.

PET-G Premium: differences between the page and 2022 PDF

The reviewed Spectrum page lists a 230–260°C nozzle, 60–80°C bed, 40–350 mm/s speed and 75–100% cooling. Its 2022 PDF lists 230–255°C, the same 60–80°C bed, 40–120 mm/s speed and active cooling up to 100%. The PDF bases settings on a 0.4 mm nozzle and ties some ranges to geometric complexity. Do not combine one version's temperature limit with the other's speed to invent a single resolved profile. Record both versions and confirm which applies to your reference.

The page lists enclosure and dryer as unnecessary, along with no requirement for a ruby or hardened nozzle. The PDF also says those items are not required. That describes this grade in these documents; it is not an inventory of every current printer's capabilities. The PDF calls for dry room-temperature storage, protected from moisture, sunlight and direct heat. Consequently, “dryer not required” does not remove its storage guidance. It also does not prove the condition of a particular opened spool.

Spectrum presents low moisture absorption and practically zero shrinkage as product advantages. Keep these attributed: they are not independent measurements on your spool. The page says bed adhesive is unnecessary and names products for increasing adhesion or limiting warping if needed. Before purchasing, identify the grade, color and applicable document instead of extending these instructions to all PETG. The PETG page broadens the discussion of the family without resolving the differences between the two Spectrum documents.

Prepare a visual comparison without inventing results

Start by defining the part's function and viewing conditions. You could compare models of the same geometry while retaining each grade's confirmed profile. This is a proposed comparison, not a standardized method or proof of equivalent manufacturing. Record profile differences instead of claiming that material alone has been isolated. No printing result is supplied here. Keep a record of what you changed and what you observed so a useful result is not mistaken for a transferable property of the whole polymer family.

Spectrum's suggestion about few outer perimeters can become a variable to examine. It does not establish that a solid block is always less transparent, that a particular wall is sufficient, or that a smooth build surface necessarily improves the result. Likewise, Polymaker's textured-PEI recommendation is manufacturing guidance without an associated optical measurement in these documents. Keep the accepted printing surface separate from the visual criterion being evaluated. Do not replace a documented adhesion instruction with an optical recommendation that these sources do not provide.

If you observe bubbles, haze or strings, record the defect and conditions before concluding why it happened. The collected sources do not establish that those signs automatically prove moisture or a single cause. Compare storage and drying with the grade instructions; the filament-dryer page develops that subject. A satisfactory visual trial does not, by itself, demonstrate thermal or mechanical suitability of the cover. Different acceptance criteria require their own evidence rather than a conclusion based solely on appearance.

Decide using checks specific to the project

For a backlit sign or semi-transparent housing prototype, PET-G Premium is a candidate named by Spectrum. That commercial application statement does not validate your geometry, fasteners or light source. Record the actual requirements before ordering a spool. The label “low-power LED” alone provides neither part temperature nor an acceptance threshold establishing PETG suitability here. Treat the suggested application as a starting point for selection and retain any missing thermal or mechanical information as an open question.

To examine PolyLite PC, compare published guidance with documented printer limits and the intended profile. Have the enclosure wording clarified if it determines your choice. Higher figures in some thermal entries do not remove the need to check methods and application requirements. The useful question becomes: which data are missing to choose this grade for this part? It cannot be answered by the PC or PETG category alone. Nor does the existence of a heated bed establish that all other printing conditions are met.

Finally, record the chosen document and date, applicable settings, intended appearance and criteria still requiring verification. For Spectrum, keep the page/PDF differences visible until resolved for your reference. For Polymaker, retain the limitation on optical specimen preparation. Other grades can be explored through PCTG vs PETG without presuming they solve a thermal requirement. Selection can then follow explicit requirements and evidence, rather than a generic transparency promise or an unverified claim that one family always suits the application.

Sources and limits

• Polymaker — PolyLite PC technical data, methods and typical-value limitations
• Spectrum — PET-G Premium product page
• PolyLite PC Technical Data Sheet V5.4
• Spectrum PET-G Premium Technical Data Sheet (prepared 06-04-2022)

We organize manufacturer and community documentation; we have not measured these products ourselves. The manual for your exact model takes precedence over general guidance.