Water-resistant or waterproof? The difference that changes everything
Water-resistant refers to the material itself. A water-resistant filament absorbs little to no water, so it won't swell, weaken, or warp when it gets wet. PETG and ASA are water-resistant: you can safely let them get wet without the material suffering.
Waterproof refers to the print as a whole. A print is only waterproof if no water leaks through it. And that’s where the problem lies: an FDM print is built up in layers, and there are microscopic gaps between those layers.
Even with a water-resistant material, water can seep through those layer seams. A PETG container is water-resistant, but not automatically waterproof. However, with the right print settings and post-processing, you can get pretty close.
The best water-resistant filaments
For an application that will get wet, choose a material that doesn't absorb moisture. Two filaments stand out.
1. PETG: the practical all-rounder
PETG is the best choice for most people. The material is related to the plastic used for drink bottles, and just like those bottles, it is naturally water-repellent.
It absorbs almost no water, retains its strength when wet, and is often food-safe (though this varies by brand).
On top of that, PETG is easy to print: it adheres well, barely warps, and doesn't require an enclosed printer. For a planter, a splash-proof housing, or a container that needs to withstand moisture, PETG is the logical first choice.
2. ASA: the strong alternative
ASA is just as water-resistant as PETG, but it’s also stronger and stiffer. It’s less prone to warping on larger prints and is a great choice for parts that need to withstand moisture as well as higher temperatures and mechanical stress.
A downside of ASA is that it’s more demanding to print. You’ll want to print it in an enclosed printer cabinet. For pure water resistance, PETG is usually the easier choice. Choose ASA if your print also needs to handle heavier mechanical loads.
These materials are not a good choice
Nylon sounds like a strong candidate because it’s tough and wear-resistant. However, nylon is extremely hygroscopic: it actively absorbs moisture from the air, and it does so quickly.
A nylon print will keep absorbing water, causing it to expand slightly and lose its stiffness. That’s the exact opposite of what you want for a wet application.
PLA is the most popular filament, but it’s unsuitable for moisture. It’s porous at a microscopic level, absorbs water slowly, and can eventually weaken and expand.
For a print that only gets splashed occasionally, it’s fine, but for structural use in wet conditions, PLA is a no-go.
How to make a 3D print waterproof
Chosen the right material? You’re not there yet. A print only becomes waterproof based on how you print and finish it. These steps make all the difference.
Make the walls thicker. The more material on the outside, the less chance of leaks through the seams. Aim for a wall thickness of about 1.5 mm, or three to four perimeters (outer walls) in your slicer.
Increase the flow slightly. By slightly increasing the amount of material the printer extrudes (around 105% for the walls and the top and bottom layers), you press the layer seams closer together. This leaves less space for water to seep through.
Pay attention to your infill for solid parts. For a waterproof wall, the exterior is what matters most, but for thin objects, a higher infill to make the print more solid and therefore denser.
Finish with a coating. The surest way to make a print watertight is to apply a layer of epoxy or a water-resistant varnish to the outside. This completely seals the layer seams and acts as a shield. For applications that absolutely cannot let a single drop through, this is the step that makes the difference.
With the right combination of material, settings, and finishing, you get a print that keeps water out, even under prolonged exposure.
Which filament should you choose and when?
Choose PETG for the vast majority of wet applications: planters, housings, containers, and anything that needs to be moisture-resistant and easy to print.
Choose ASA if your print needs extra strength or heat resistance in addition to moisture resistance, and you don't mind a slightly more demanding printing process.
Avoid nylon and PLA for wet applications. Nylon absorbs moisture, and PLA is porous.
Not sure about your specific project? Use our material selection guide or let us take a look with a free printability check.
Frequently asked questions about watertight 3D printing
Which filament is the most water-resistant?
PETG and ASA are the most water-resistant commonly used filaments. They barely absorb any moisture and retain their properties when wet. PETG is the easiest to print, while ASA is stronger and more rigid.
Is a 3D print automatically watertight?
No, because an FDM print is built up in layers with tiny seams between them, which water can seep through. Even with a water-resistant material, you need to use thicker walls, higher flow, and possibly a coating to make a print truly watertight.
Is PLA waterproof?
PLA is not waterproof. The material is porous and slowly absorbs water, which can cause it to weaken and expand over time. It’s fine for occasional contact with water, but for structural use in wet conditions, you’re better off choosing PETG.
Is a PETG print waterproof?
PETG is water-repellent, but a PETG print isn't automatically watertight. Water can penetrate through the layer seams. You can make a PETG print watertight by using thicker walls, a slightly higher flow rate, and potentially a coating.
Get your waterproof print made
Know which material you need? Upload your STL file to our 3D print price calculator and calculate the cost instantly. Both PETG and ASA are available. Just mention in the notes that the print needs to be as watertight as possible, and we’ll take that into account with our print settings.
Don't have a file yet, or unsure about the right material for a wet application? Request a free printability check and we’ll take a look with you.
