What Is PETG, And Why Is It So Widely Used?
PETG, standing for polyethylene terephthalate glycol, is a thermoplastic polyester. This means when PETG is heated, it can be molded into any shape you might need, and as it cools off, it hardens and maintains the shape it was formed into.
PETG has many favorable properties that make it an incredibly useful and versatile material. It's astoundingly strong and durable so it's resistant to impact and high pressures. And not only is it resistant to heat, but it's also resistant to harsh chemicals, not to mention its waterproof and remains stiff in all but the harshest environments.
Knowing this, it’s no wonder that PETG has become one of the most common filaments used in 3D printers today. PETG’s general affordability, as well that fact that it's easily recyclable and non-toxic, allow it to be used in all sorts of products and applications.
Outside of 3D printing, PETG is still everywhere. You most likely have more than one product made from PETG in your house right now. One of its most common uses is in food and drink containers, like water bottles and take-out containers. PETG is non-toxic and food safe. That along with the fact that it's cheap and easily recyclable, makes PETG the perfect material for any container made for holding food.
PETG is also used in medical device packaging and medical implants. PETG is clear and easily colorable so it's the perfect material for the packaging of any product. PETG’s rigid structure also means that it can withstand the harsh measure used to sterilize medical instruments, making it incredibly useful in medical implants and countless other medical tools and devices.
How Heat Resistant Is PETG?
Before we get into the details of exactly how heat-resistant PETG is, it's useful to make sure that we understand exactly what we are measuring.
Melting point is most likely the first thing that you think of when thinking about how resistant to heat something is. As you know, the melting point of any material is the temperature at which the material begins to transition from a solid to a liquid. While this can be a useful piece of information, this isn’t the number we look at when determining how heat-resistant something is.
Imagine you have some sort of tool like a wrench. If the wrench melts and becomes a liquid, it is completely unusable, and for all intents and purposes, it is no longer a wrench. Though the material that made up the wrench still exists, it will no longer be of use to you, and in fact, it would have stopped being usable a long time before that. A wrench will begin to bend from heat much before it turns into a puddle, but a wrench that bends when force is applied is no more useful than the liquified wrench from before.
Therefore the temperature we will be looking at is the glass transition temperature. The glass transition temperature of a material is the point at which it will begin to lose its shape and rigidity. You can think about it as a blacksmith hammering a sword he is forging. The blacksmith heats up the sword to the point where he is able to bend and manipulate the metal, but it never completely turns into a liquid, just a less rigid solid.
This is the temperature you want to look at when determining the heat resistance of a material. We want to know how hot the object can get before it starts bending and breaking and losing its shape.
For reference, the melting point of PETG is around 240° C. This is the point at which it would start turning into a liquid. However, the temperature we will be paying attention to, the glass transition temperature, is much lower at around 85° C.
How Does PETG Compare To Other Materials?
So we’ve established that PETG is quite good when it comes to resisting heat, but how does it stack up against some of the other options like PLA and ABS?
PETG Vs. PLA
PLA, or polylactic acid, is another thermoplastic made from organic materials like corn starch. Just like PETG, PLA is commonly used in the food and medical industries, however mostly in products that need to be biodegradable and break down over time. PLA is also one of the most commonly used materials in 3D printing, but how does its heat resistance compare to PETG’s?
Though there are types of PLA specifically made to be more heat resistant, normal PLA has an average glass transition temperature of about 60° C (140° F). This is far lower than PETG’s glass transition temperature of 85° C, which means that even though PLA is another great material for 3D printing, PETG is far superior if your print needs to be heat resistant. PLA should not be used if you are planning for your print to be exposed to hot environments for extended periods of time.
PETG Vs. ABS
ABS, or Acrylonitrile butadiene styrene, is another thermoplastic that is commonly used in 3D printing. Though not nearly as good for the environment as PLA, ABS is cheap to produce and incredibly versatile, making it a great option for any kind of project you might think of. ABS is strong, resistant to impact and chemicals, and performs well in high and low temperatures.
These properties allow ABS to be used in many different applications. Though it does have much use to the food industry as PETG and PLA do, ABS is used in all sorts of products, including musical instruments, car components, computer keyboards, and, most famously, lego bricks. So how does PETG’s heat resistance compare to that of ABS?
Though PETG is a good heat-resistant material, ABS far outmatches it in this department. The glass transition temperature of ABS is about 105° C (221° F). This is a whole 20 degrees celsius more than PETG. Because of this, if you are planning to print something that will be exposed to extreme heat for extended periods of time, ABS is the superior option to PETG.
