Melting point and glass transition temperature influence 3D printer temperature settings.
In the world of 3D printing, PETG (polyethylene terephthalate glycol) is among the more popular filaments and is known for a combination of good printability, resistance to warping and shrinkage, and smooth surface finish. Other notable properties of PETG are good impact resistance, chemical resistance, water resistance, and UV resistance.
Before we dive into the significance of the PETG melting point—which influences one of the most important print settings—here’s a bit more background about the 3D printing filament. The first thing to know about PETG is that it is based on PET (polyethylene terephthalate), one of the world’s most widely consumed plastics.
You can find PET virtually everywhere: it is used to manufacture plastic water bottles and most plastic consumer packaging. PETG, for its part, is a slightly modified version of PET (with added glycol), but shares many of the advantages of PET, such as its strength, cost, and easy processing. The addition of glycol in PETG results in a thermoplastic that is more durable.
The combination of price and good mechanical properties has led to PETG being used for many applications. It is suitable for the production of functional prototypes and tools and jigs for manufacturing. It has also been used for making end-use parts or replacement parts that require good durability and UV resistance. Many 3D printing users are also drawn to PETG because it can be transparent, which has made the filament a great option for prototyping consumer products for the packaging industry.
One of the most important things to know about PETG filament before 3D printing is its melting point. PETG’s melting point is around 260°C. In other words, when PETG is heated to 260°C, the material will fully transition from solid to liquid form. PETG’s glass transition temperature, which indicates when the material starts to soften and lose its solid structure, is 85°C, while the material can become viscous (the stage between solid and liquid) at about 230°C.
Let’s take a look at what these temperatures mean for 3D print settings.
PETG’s melting point is a critical consideration when choosing 3D print settings, particularly nozzle temperature and, if applicable, bed temperature. In the simplest terms, the material’s melting point determines how hot the printing process must be in order to achieve optimal flow rate and layer adhesion.
When it comes to printing temperature, we are primarily referring to the temperature of the print nozzle. As the filament passes through the 3D printer extruder, the heat of the nozzle melts the filament so it can be deposited smoothly onto the build plate. While PETG’s melting point is 260°C, it is typically advisable to print the filament at a slightly lower temperature, in the range between 220°C and 260°C.
Finding the right nozzle temperature is vital: if the nozzle temperature is too low, the PETG filament won’t extrude properly and risks clogging the hot end. On the flip side, if the printing temperature is too high, the 3D printer filament will flow too rapidly and cause print defects such as stringing and blobs.
Recommended reading: PETG stringing: What it is & how to prevent it during 3D printing
In the case of PETG, which has a relatively high melting point, it is advisable to use a 3D printer with a heated bed. Most PETG filaments demonstrate the best print quality with a heated print bed of between 65°C and 80°C. While PETG has naturally good first layer adhesion and is less prone to warping than many filaments, having a heated print bed does help by ensuring a more stable print environment temperature, which stabilizes the cooling process and further minimizes the risk of warping.
Importantly, you should not heat your print bed above PETG’s glass transition temperature (85°C). If the bed reaches this temperature, the first layers of your 3D print will not solidify properly, which can lead to structural issues.
Keep in mind that the aforementioned print settings are generalized and provide a fairly wide range of temperatures. Specific print temperatures will vary slightly depending on the brand of PETG filament you are using, so it is best to check filament manufacturer data sheets and recommendations. If you don’t have access to the filament data sheet, start with some test prints. We advise starting on the lower end of the print temperature range and increasing the nozzle and bed temperature gradually (by about 5 degrees at a time) until you reach the best print results.
Recommended reading: PETG print settings: Adjusting temperature, speed & retraction to improve printing
As we saw, PETG has a high melting point of 260°C and a relatively low glass transition temperature of about 85°C. This means that while the printing process requires higher temperatures, parts made from PETG are not known for their heat resistance. For instance, PETG cannot withstand boiling water.
PLA, which does not require a heated print bed, has a significantly lower melting temperature of between 170°C and 180°C and a glass transition temperature between 50°C and 80°C. This means that while PETG parts are more temperature resistant, they cannot withstand significantly greater temperatures than PLA before losing their strength. PETG does, however, have greater impact strength than PLA.
Recommended reading: PETG vs PLA: How do they compare?
Known for its durability and good thermal resistance, ABS has a lower melting temperature than PETG (around 220°C) but a higher glass transition temperature of about 105°C. We should point out that because it is an amorphous thermoplastic, ABS doesn’t technically have a melting point. This means that it transitions easily between a soft and hard state, instead of a solid to liquid state. In terms of other properties, ABS has a lower tensile strength than PETG and similar impact resistance. Unlike PETG, ABS is not UV resistant.
Recommended reading: PETG vs ABS: How do they compare?
In the end, PETG is a popular FDM 3D printing material with many benefits: including high strength, good bed adhesion, good resistance to deformation on the print bed, and chemical resistance. However, while the polymer has a high melting point, it has a relatively low glass transition temperature, which can influence the applications it is viable for. For instance, PETG may not be a great material for applications that require strength and durability in high temperatures exceeding 85°C.
Here are some of the key takeaways from this article:
PETG is based on PET, one of the most commonly used plastics in the world.
PETG’s melting point is 260°C, while its glass transition temperature is significantly lower at 85°C.
When 3D printing PETG, a heated print bed between 65°C and 90°C is advisable.
The optimal nozzle temperature for PETG filaments is between 220°C and 260°C.