PETG is celebrated for its versatility, but the path to perfect prints can be paved with minor pitfalls, such as stringing or adhesion issues. Unlike PLA, which is quite forgiving, PETG requires more careful preparation and correct settings. This article is a practical guide that will show you how to tame this material and achieve consistently great results. We will walk you through hardware preparation, optimal slicer settings, and troubleshooting common problems.
Preparation is Key: Hardware and Filament Drying
Before you even send the first G-code to the printer, it’s crucial to ensure that both your hardware and material are in optimal condition. For PETG, this is doubly true.
Do I need a special printer?
The good news is that you don’t need any exotic or expensive printer to print with PETG. Most modern FDM printers can handle it. However, there are two key hardware components that are essential for successful printing:
- Heated Bed: This is practically a necessity. PETG requires a bed temperature in the range of 70–90 °C to ensure proper first layer adhesion and minimize warping.
- Hotend: PETG prints at temperatures of 230–255 °C. Most hotends with a Teflon (PTFE) tube can handle this range, but it is at the limit of their safe use. For long-term and reliable printing, an all-metal hotend is recommended, as it tolerates higher temperatures without the risk of PTFE tube degradation.
Hygroscopicity – the silent killer of print quality
The most common cause of PETG print failure is not poor settings, but moisture. PETG is hygroscopic, meaning it actively absorbs moisture from the surrounding air. Even filament unboxed from vacuum packaging can absorb enough water in a room with normal humidity within a few days to negatively affect printing.
Moisture in the filament turns into steam in the hot nozzle. These microscopic steam bubbles cause several problems:
- Popping and Sizzling: You may hear a faint popping sound during extrusion.
- Poor Surface Quality: Bubbles leave small blemishes and inconsistencies on the print surface.
- Reduced Strength: Steam disrupts layer adhesion, leading to more brittle prints.
- Stringing: This is the most visible symptom. Steam disrupts the smooth flow of plastic, significantly worsening the formation of thin strands between parts of the model.
How to properly dry PETG
The solution is drying. For serious work with PETG, investing in a filament dryer is one of the best steps to save hours of frustration and unnecessary tuning. It eliminates the main source of problems right from the start and turns PETG from “problematic” into a truly reliable material.
- Specialized Filament Dryers: The ideal solution. They maintain a constant temperature and air circulation. Some models allow printing directly from the dryer.
- Food Dehydrators: A very popular and affordable alternative. You need to remove the internal trays to fit the spool.
- Electric Oven: Usable, but with great caution. The oven must be able to reliably maintain a low temperature and have good air circulation.
Recommended parameters for drying PETG are a temperature around 65 °C for 6 to 8 hours. After drying, store the filament in an airtight box or bag with desiccant (silica gel).
The Key to a Perfect First Layer: Uncompromising Adhesion
The first layer is the foundation of every successful print. However, with PETG, the issue of adhesion is specific – often the problem isn’t that the material doesn’t stick, but that it sticks too well.
Choosing the right print surface
PETG tends to chemically bond with some surfaces, especially smooth PEI (polyetherimide). Printing directly on a smooth PEI sheet can lead to tearing off a piece of the bed surface when removing the print. Therefore, the following surfaces are strongly recommended:
- Textured Steel Sheet (Powder-coated PEI): The rougher surface provides excellent adhesion, while also allowing easy removal of the print after cooling. It is the ideal choice for PETG.
- Satin Steel Sheet: Offers a compromise between smooth and textured surfaces and also works very well for PETG.
- Glass: On clean glass, PETG can stick too strongly. A separating layer is always necessary.
Separating layer – your best friend
If you are printing on a smooth PEI or glass surface, using a separating layer is absolutely crucial. Its purpose is not primarily to increase adhesion, but rather to create a barrier between the print and the bed, preventing their permanent bonding.
- Glue Stick (Kores, PVA): A thin layer of glue applied to the bed is the simplest and most reliable method.
- Hair Spray (e.g., 3DLac): Creates a thin film that works well as a separator.
- Window Cleaner: Some users report success with simply wiping the bed with window cleaner, which leaves a slight film.
First layer calibration (Z-offset)
Unlike PLA, where the first layer is often slightly “squished” into the bed for maximum adhesion, with PETG you need to set a slightly higher Z-offset (greater distance of the nozzle from the bed). PETG does not like to be compressed too much. A nozzle set too low will cause the material to accumulate on the nozzle, tear already laid lines, and the first layer will fail. Find a height where the lines are neatly laid side-by-side, touching, but not deformed sideways.
Optimal Slicer Settings: A Step-by-Step Guide
Correct settings in your slicer (e.g., PrusaSlicer, Cura) are crucial for the quality of the final print. Here are the key parameters to focus on. To start, it’s always good to use the default PETG profiles included in modern slicers and then fine-tune them.
Nozzle and bed temperatures
- Nozzle Temperature (Hotend): Typically ranges from 230–255 °C. Higher temperatures (e.g., 240-250 °C) generally lead to better layer adhesion and thus a stronger print, but may slightly worsen overhang printing and stringing. Lower temperatures can improve details, but at the cost of weaker layer adhesion. It is recommended to start in the middle of the range recommended by the filament manufacturer.
- Bed Temperature: The standard range is 70–90 °C. For the first layer, a temperature 5-10 °C higher is often used to ensure maximum adhesion.
Print speed
PETG prefers slower printing. Too high a speed can lead to insufficient material melting, poor layer adhesion, and generally worse surface quality.
- General Print Speed: It is recommended to stay within the range of 30–60 mm/s.
- First Layer: Always print slower, ideally 20–30 mm/s, to allow the material enough time to adhere to the bed.
- Travel Speed: Conversely, travel speed should be as high as possible (e.g., 120 mm/s and more) to minimize the time during which molten plastic can leak from the nozzle and cause stringing.
Cooling
Cooling settings for PETG are a crucial compromise between detail quality and mechanical strength.
- For maximum strength: Reduce cooling to a minimum or turn it off completely (except for bridges and overhangs). Slower cooling allows layers to bond better thermally.
- For best details and overhangs: Cooling is necessary. A good compromise is to set the fan to 30–50% power.
- First Layers: Always print the first 1-3 layers without cooling to prevent shrinkage and detachment from the bed.
Retraction – key to combating stringing
Properly set retraction is the most important tool for eliminating stringing. If the problem persists even after drying the filament, focus on these parameters.
- Retraction Distance: Depends on the extruder type.
- Direct Drive: 0.5–2 mm.
- Bowden: 3–5 mm.
- Retraction Speed: Usually between 25–40 mm/s. Too high a speed can cause “grinding” of the filament in the drive gear.
- Z-hop (Lift Z): A slight lifting of the nozzle during travel can help, but sometimes it can worsen stringing. Use with caution.
- Wipe: A function that “wipes” the nozzle against the edge of the model before travel is very effective for reducing stringing.
