watertight vs waterproof 3d printing

Are 3D Printed Parts Watertight?

Waterproof vs Watertight 3D Printing

Are 3D Prints Watertight?

Let’s start by clearing up two commonly conflated terms: waterproofness and watertightness. Waterproofness is a material property that pertains to a given material’s inherent ability to resist water permeation. Watertightness, on the other hand, refers to an object’s ability to hold water without leaking, and has more to do with the construction of the object than anything else.

So, can 3D printing produce watertight parts?

The simple answer is yes! 

The more complex answer is that certain technologies, like stereolithography (SLA), can produce watertight parts straight off the printer. Selective laser sintering (SLS) and multijet fusion (MJF) also produce parts with some level of inherent water resistance. Other technologies, fused deposition modelling (FDM) for example, require a bit more consideration to be put into design choices, and may also require some post-processing. 

Check out this table for a quick overview of the watertightness of parts produced with the most popular 3D printing technologies. For more detailed information, continue reading below

 

SLA

SLS/MJF

FDM

Watertight off the printer?

Yes

Possible with specific design considerations. Post processing is recommended (see below).

Possible with specific design considerations. Post processing is strongly recommended (see below).

Best material option(s)

Accura Xtreme White,
Accura Clearvue

Nylon PA 12

ABS, ASA

Post-processing option(s)

Not required but  resin or silicone coating can be used for added protection.

Resin, silicone, or acrylic coating.

Resin, silicone, or acrylic coating.

Solvent smoothing.

 

How Do I Make a Watertight Part?

Watertight 3D Printing

The watertightness of 3D printed parts depends on a few main factors, starting with part design. 

The first step to improving the watertightness of parts produced with any 3D printing technology is to design with watertightness in mind. One method with minimal impact on part design is to reinforce the physical barriers of your part. Increasing wall thickness and the number of perimeters/shells are both good options for doing this.

If your part allows for it, modifying your design to have a more even pressure distribution will also improve watertightness by reducing areas of stress concentration that are more prone to leaking. This can be achieved by rounding off corners and edges, opting for simple and smooth surfaces, or even moving towards a more spherical design rather than a rectangular one.

3D Printing Infill Density

Forge Labs’ industrial FDM printers can be configured to improve watertightness in the following ways:

  • Increasing infill density (i.e. printing in solid rather than sparse infill) to reinforce physical barriers 
  • Extruding thicker layers (i.e. printing with a larger diameter tip) to reduce the number of layer seams and thus the possibility of interlayer gaps
  • Printing in a heated environment to improve layer adhesion and reduce the possibility for interlayer gaps

Post Processing Watertight Parts

If the part design or the selected printing technology makes it difficult to produce a watertight part straight off the printer, or if you’re looking for an added layer of protection, post-processing options exist. An epoxy resin coating is a common option for SLA, SLS/MJF, and FDM parts. Brush-on products such as XTC-3D exist specifically for 3D printed parts. Silicone and acrylic coatings are available as well. 

For FDM parts made of ABS or ASA, there is the additional option of solvent smoothing. In this case, a solvent (commonly acetone), is used to lightly dissolve and fuse the surface layers of an FDM part. In addition to producing watertight parts, this will also result in a smooth and glossy exterior finish with no visible layer lines. However, as the external surfaces are being dissolved (i.e. become thinner), solvent smoothing is best suited for parts with a wall thickness of at least 2-3 mm. Small and/or thin parts are prone to deformation.

It’s important to understand that any coating or solvent smoothing will affect final part geometry and tolerances.

FDM Vapor Smoothing

On a final note, though we stated at the top that watertightness is a function of part geometry more than anything else, selecting a material with natural water resistance will help with achieving watertightness.

For SLA and SLS/MJF, our most popular materials (Accura Xtreme White and ClearVue for SLA; Nylon PA 12 for SLS/MJF) are all good options. For FDM, we recommend ABS or ASA as they are less hygroscopic (i.e. less prone to absorbing moisture from the environment) than other common materials like PLA. Plus, ABS and ASA can both be post-processed via solvent smoothing.

If your part will be interacting with a liquid other than water, it’s a good idea to check for specific chemical resistance as well. SLS/MJF produced Nylon PA 12 parts, for example, are resistant to many common chemicals including alcohol, motor oil, and most alkalies.