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Do PLA Prints Absorb Water After Printing?

Choosing a filament for your 3D printing projects is a lot more complicated than one might think. Most of the time, we 3D printers default to PLA filament, the most cost-effective, easy-to-use filament out there. But as you might know, PLA absorbs water, which might make it unsuitable for prints that’ll hold liquids. 

PLA prints absorb water after printing in very small amounts. This is because PLA naturally absorbs moisture, weakening the material over time. However, unmodified PLA degrades fastest in hot water, and it could take years for it to break down if you don’t completely submerge it in water. 

The relationship between PLA filament and water is tricky, so let’s get into the details and talk about how PLA reacts with water. Then, I’ll teach you what to expect from this filament when you submerge or fill it with a liquid, and I’ll also give you some tips for creating PLA prints that’ll stand up to water and moisture exposure. 

Is PLA Waterproof After Printing?

If you’ve researched PLA and how it reacts with water, you may know that you have to dehydrate PLA before you print with it. 

That’s because PLA is a hygroscopic material that draws in moisture from the air, causing it to swell and become more brittle. 

Still, have you ever wondered if printing with a filament such as PLA will change its capacity to absorb liquids? Well, I’ve been there too, and here’s the scoop. 

PLA isn’t waterproof after printing. This is because PLA naturally absorbs water, and filaments don’t change their ability to absorb water after printing with them. So if a material isn’t waterproof before you print a model, it’ll never be waterproof. 

So, the properties of your filaments will never change. When you choose a 3D printing material, you’re stuck with all of its shortcomings and strengths. 

In the case of PLA, that means that your print will always absorb water and swell when you expose it to liquids, which could make the object more brittle. 

Do PLA Prints Dissolve in Water?

One of the best things about PLA is that it’s a bio-based filament. PLA is made of plant starches from crops such as corn and potatoes, making it safer for the environment. 

These materials are biodegradable, and if you’ve ever cooked potatoes or corn, you know that they get softer when you submerge them in hot water. However, they get more rigid and dense in cold water. 

Since PLA contains these organic ingredients, it reacts similarly to water. Of course, PLA won’t immediately dissolve in water. But when the conditions are right– namely, when you put it in hot water for a long time– will it turn into a clump of mashed potatoes?

PLA dissolves in water if the conditions are right and if there aren’t preservation additives in the filament. For example, PLA will dissolve faster if the water is hot or contains microorganisms that decompose starches. However, it is chemically biodegradable, meaning the process is very slow.

If your PLA isn’t in hot water, or if you use a filament that contains additives to help preserve it, you probably won’t have to deal with decomposition, even if you use the print for collecting water. 

In fact, it’s estimated that PLA would last in the water for hundreds of years.

Factors That Make PLA Prints Dissolve in Water

So, many factors are at play when determining how long PLA will last when exposed to water. Let’s take a look at them in detail: 

No Additives in the PLA

The most determining factor in how long a PLA print will last in water is how many additives are in the filament. 

For example, some manufacturers add plasticizers to PLA to make it last longer and resist breaking, even after it has absorbed water. 

So, raw PLA will fall apart much faster than enhanced PLA. 

High Water Temperature

When you submerge PLA in room-temperature water or cold liquids, it can take years for it to fall apart. However, in hot water, you’ll start to see it fall apart within about a week. 

That’s because hot water can melt the plastic a bit and make it softer, allowing water to permeate throughout the PLA. As this process happens, the water will disintegrate the starches in the filament, breaking the polylactic acid chains that keep it together. 

The PLA will start to chip, break, and become very brittle as this occurs. Also, if you leave it in hot water long enough, your PLA print will become one with the water, creating a foggy film. 

Poor Water Quality or Bacteria

Water quality also comes into play here. As I mentioned before, PLA is plant-based, and organisms like to eat plants. That’s why plants decompose, after all. 

So, if you put PLA in water such as pond water or aquarium water, it’ll break down much faster than if you put it in distilled water. That’s because there are millions of tiny, hungry bacteria and other organisms in the water who are willing to make a snack out of your PLA print. 

To see PLA degradation in action, check out this fantastic PLA water-decomposition experiment YouTube video from Makers Mashup: 

Tips To Keep PLA From Absorbing Too Much Water

So, as we now know, PLA and water have an extremely complicated relationship. There are many things at play here, but there are plenty of easy ways to keep your PLA prints strong, no matter how much water you expose them to. 

Let’s look at how you can keep your PLA prints from absorbing too much water: 

  • Print thick layers. Thick layers have better layer adhesion, which will help your printed object repel water for a longer time. In addition, even if the model absorbs moisture, a thick layer will make the PLA tougher to break, preventing brittleness. 
  • Waterproof your PLA prints. Waterproofing comes in many shapes and sizes, such as wax, UV resin, polyurethane, or acrylic sealant. However, most of these treatments aren’t food-safe, so don’t use them for drinking, eating, or aquarium parts. 
  • Use high-quality PLA. Higher quality PLA with additives in it will last much longer, even when you constantly expose it to humidity and water. 
  • Give your prints time to breathe. Whether you live in a humid environment or want to use your PLA to make coasters and vases, letting your PLA naturally dehydrate will keep it strong. So, don’t leave water on the PLA any longer than necessary and keep it in a dry place to prolong its life. 

Final Thoughts

PLA is a hygroscopic material that draws in moisture, which eventually causes the material to degrade. As a result, PLA prints absorb just as much water as PLA filament does. 

However, PLA will last many years if you keep it away from hot water and don’t expose it to water with bacteria or microorganisms in it. In addition, using a filament with preservatives and strengthening additives can help it last longer, no matter how humid or wet it gets. 

If you want to use PLA prints to contain water, be sure to print thick layers, waterproof them, and use high-quality PLA.