Does PLA Shrink While 3D Printing? (How to Compensate?)

Shrinkage is a natural side-effect of 3D printing due to how thermoplastics behave when we rapidly cool them down after bringing them up to very high temperatures, meaning that there isn’t much we can do to prevent it.

On the other hand, as each thermoplastic has a distinct chemical composition, the severity of shrinkage shows significant amounts of change between different materials, to the point where we can sometimes entirely disregard the shrinkage.

Today, we will discover whether PLA plastic shrinks more than what we deem negligible during the 3D printing process, which is a vital point to consider in projects where dimensional accuracy is paramount, such as printing a part that needs to be an exact fit.

So, does PLA shrink during the 3D printing process?

While PLA shrinks like any other thermoplastic during the 3D printing process, it is the filament that shrinks the least in the realm of 3D printing with a shrinkage rate of 0.2% to 0.3% on average.

As a result, shrinkage will most likely be negligible for smaller models (unless you require high precision) and easily compensable for larger ones.

Next up, we will dive deeper into the topic of PLA shrinkage, find out the shrink rate of PLA, examine the methods we can use to compensate for the shrinkage, and discuss how shrinkage affects the printing process.

Does PLA Shrink While 3D Printing?

Even though you may never notice it in smaller prints, especially with filaments that have lower shrink rates, shrinkage is, without a doubt, a phenomenon that affects all types of thermoplastics during the 3D printing process in varying degrees.

Like any other thermoplastic that undergoes thermal expansion and contraction due to fluctuations in temperature, PLA does also shrink during the 3D printing process due to these phenomena, which is practically unavoidable due to how thermoplastics work.

To understand how the shrinking process occurs, let’s take a quick look at what happens to the filament during the 3D printing process.

At first, the plastic starts melting due to coming into contact with the high temperatures of the nozzle, causing it to expand due to the phenomenon of thermal expansion where the thermoplastic changes its shape as a result of the temperature change.

When the plastic leaves the nozzle and comes into contact with the build plate, it rapidly starts cooling down, which causes it to shrink due to thermal contraction, where the thermoplastic once again changes its shape as a result of the temperature change, but this time, in the opposite direction.

Finally, upon stabilizing the temperature, the plastic often becomes smaller than intended due to the contraction, which we call the shrinking of the plastic.

What Is the Shrink Rate (Percentage) of PLA?

As the shrink rate varies between different materials, knowing the shrink rate of the material you’re printing with is vital to perform the necessary calculations to compensate for the difference.

On average, PLA shrinks between 0.2 percent to 0.3 percent, making it the filament type that shrinks the least compared to other popular alternatives such as PETG and ABS.

To put things into perspective, let’s take a look at two examples of how shrinking impacts models of varying sizes:

For a 20 mm calibration cube, a 0.2% shrinkage rate would mean that the model would end up being 19.96 millimeters on each side, with a barely noticeable 0.04-millimeter loss.

On the other hand, for a larger 100 mm cube, the same shrinkage rate would cause each side to be 99.8 millimeters, yielding a 0.2-millimeter loss.

Please note that it’s always best to calculate the shrinkage rate of the filament you use specifically, as the figures can show variance depending on the material composition of the spool of PLA you’re using.

How to Compensate for PLA Shrinkage?

Compensating for the shrinkage of the material allows you to stay unaffected by the dimensional inaccuracy that occurs due to the shrinkage and make it so that your model has the desired dimensions.

The best way to compensate for PLA shrinkage is to increase your model’s dimensions by the amount of shrinking you have observed on the model you have printed.

By configuring the model to be slightly larger than intended, you will cause the shrinking to bring the model’s dimensions down to their intended values instead of making them smaller than expected, which will successfully compensate for the shrinkage.

As it’s vital to calculate the actual amount of shrinkage that your model undergoes for this strategy to work, let’s find out how we can obtain this value before adjusting the dimensions for compensation.

  1. Perform a test print with the original dimensions of your model.
  2. Measure your model’s dimensions for all sides, and write them down.
  3. Divide each value you have measured by the intended dimension values entered into the slicer.
  4. Multiply each value with 100, and subtract the values you have found from 100.

To make the process clearer, let’s go through a quick example of where you intended to print a 20 mm cube, but the measurements of the cube showed you that the cube’s actual dimensions are 19.5 mm on each side. 

To start, let’s divide 19.5 by 20 (step 3), which will give us the value of 0.975.

Multiplying this value with 100 will yield 97.5, and subtracting this value from 100 will give us the number 2.5 (step 4).

In this case, our shrinkage rate is 2.5%.

To compensate, we need to find the value where a shrinkage rate of 2.5% would bring the actual dimensions of the model down to the intended 20 mm, which we can quickly find with this equation:

x * (1 – (2.5/100)) = 20

x = 20.512

As a result, inputting the dimensions of 20.512 mm into the slicer would allow us to obtain a cube with actual dimensions of 20 mm, assuming that the shrinkage rate is 2.5%.

How Does PLA Shrinkage Affect the Printing Process?

Having an idea of how the shrinkage of the plastic affects the printing process and the final product is paramount for identifying the situation and applying a suitable solution for compensation.

Even though such a low shrinking rate (in the case of PLA) means that you most likely won’t notice the shrinkage at first look, the actual dimensions of the model do end up being lesser than the dimensions on your screen, making the object slightly smaller than it should be.

While this may not be something to think about for most prints, parts that require exact dimensions will be negatively affected by the shrinking regardless of how little it is, making it a vital point of consideration for such scenarios.

Fortunately, as it’s possible to compensate for the shrinkage as long as you are aware that it exists, the shrinking is more of a nuisance rather than a critical problem.

Wrapping Up

While it’s impossible to prevent PLA from shrinking during the 3D printing process, compensation by calculating how much the plastic will shrink is more than enough to obtain the intended dimensions for the model and achieve a successful print.

To quickly recap, even though PLA shrinks the least of all the commonly used filaments in 3D printing with a shrinkage rate that falls between 0.2% to 0.3% on average, we would be wrong to say that it does not shrink.

Fortunately, such a low shrinking rate makes it even easier to compensate for the shrinkage, as printing the model to be larger by such small margins won’t have any considerable effect on the print time or the amount of material you use.

Happy printing!