What Is the Shrinkage Rate of PETG? (How to Compensate?)

Shrinkage is a phenomenon that affects all kinds of plastic due to the thermal contraction and expansion that takes place during the 3D printing process, where the material rapidly heats up and rapidly cools down in a short amount of time.

That being said, due to the differences in the properties of the materials, while some 3D printing filaments shrink in considerable amounts, the rate of shrinkage is negligible for others, making the shrinkage rate a vital point to consider before printing your model.

Today, our topic will be the shrinkage of PETG filament, in particular, where we will observe how much PETG shrinks due to the 3D printing process and what you can do to compensate for the shrinkage.

So, what is the shrinkage rate of PETG, and how to compensate for it?

While the exact figure can vary between different brands of PETG filament, the shrinkage rate of PETG falls between the range of 0.3% to 0.6% in most scenarios.

To compensate for the PETG shrinkage, we recommend scaling your model up by the shrinkage rate, which will act as a way to negate the dimensional change that occurs due to the shrinking of the plastic.

Next up, we will take a deeper look into the shrinkage of PETG, discuss how you can compensate for PETG shrinkage in greater detail, and find out how the shrinkage rate of PETG affects the 3D printing process in real-life scenarios.

What Is the Shrinkage Rate (Percentage) of PETG?

The shrinkage rate of PETG is something you should always keep in mind before you proceed with the printing process, as a dimensionally inaccurate model will be a waste of both time and material in most scenarios.

PETG is one of the materials that don’t overly shrink, with a varying 0.3% to 0.6% shrinkage rate depending on the exact PETG filament you use.

As the actual concentration of PETG between different filaments can show a high degree of variance (with low-end brands usually using less pure PETG and more filler material), running your own experimentations to find the real shrinkage rate will yield the best results.

What causes PETG not to shrink way too much primarily has to do with its thermal properties of how much it thermally expands and how much it thermally contracts, as these properties essentially determine what we call the shrinking rate of the material.

How to Compensate for PETG Shrinkage?

Compensating for PETG shrinkage is vital to ensure that the model you print has the dimensions that you have originally intended, which is especially significant for functionally printed parts where dimensional accuracy is crucial.

To compensate for the shrinkage that occurs while printing with PETG, we recommend scaling your model up in the slicer software by the shrinkage rate of PETG.

By doing so, you will print a model that is slightly larger than its original dimensions, and the difference in the size will negate the effects of the shrinkage, causing your model to retain its actual dimensions.

That being said, as successfully compensating for PETG shrinkage is primarily about finding the real shrinkage rate value, we highly recommend running a test print with the original dimensions of your model first instead of using the assumed shrinkage rate values.

To find the real shrinkage value, all you have to do is measure your model, note the dimensions down, and then compare these dimensions to the original values you have inputted into the slicer software.

Here are the steps you can follow for the calculation:

  1. Divide the measurements you took by the original dimension values.
  2. Multiply the value you have found with 100.
  3. Subtract the value you have found from 100.

For instance, let’s assume that you were planning to print a 40x40x40 cube, and the measurements you have made showed you that the actual object has dimensions of 39.8×39.8×39.8.

In this case, we will divide39.8 by 40 to find 0.995, multiply this figure with 100 to get 99.5, and then, finally, subtract this value from 100 for a value of 0.5%, which is our shrinkage rate.

How Does PETG Shrinkage Affect the 3D Printing Process?

Understanding how PETG shrinkage affects the 3D printing process and your 3D printed model is a vital part of identifying the problem before moving on to taking the necessary steps for compensation.

In a nutshell, the observable effect of PETG shrinkage is a reduction in the dimensions of your 3D printed model, where your model becomes slightly smaller than the original dimensions you input into the slicer.

Two things contribute to shrinkage, which is thermal expansion, and thermal contraction.

First, the plastic thermally expands due to the extreme temperatures of the nozzle, meaning that the plastic is actually larger than it should be while it’s in its melted state.

When the plastic makes its way out of the nozzle and onto the build plate, it rapidly cools down due to the ambient temperature and the build plate temperature (which are much lower than nozzle temperature), causing what we call thermal contraction.

After the thermal contraction, the plastic becomes dimensionally smaller than it was in its melted state, which we call shrinking.

Does PETG Shrink More than PLA?

The shrinkage rate is definitely a factor that goes into filament selection, meaning that we certainly have to take a look at how PETG compares to PLA as the two most popular filaments in the 3D printing scene right now.

The shrinkage rate of PLA is around 0.2% to 0.3%, which is slightly less on average than the range of 0.3% to 0.6% for PETG, indicating that PETG does indeed shrink more than PLA.

That being said, the difference in shrinkage between these two filament types is minor, meaning that you can effortlessly compensate for the shrinkage while printing with either of them.

Wrapping Up

Even though shrinkage is not something that we cannot escape in 3D printing, compensating for the shrinkage, especially for a type of filament such as PETG, where the shrinkage rate is considerably low, is not too difficult.

To quickly recap, we can say that PETG has a shrinkage rate of 0.3%-0.6% in most scenarios, but the precise figure depends on the exact PETG Filament you use due to differences among brands.

Compensating for the shrinking is as easy as scaling your model up by the shrinking rate, but you may require a few test prints until you find the definite value that provides you with the exact measurements you need.

Happy printing!