3D prints made by an FDM 3D printer are usually not inherently watertight. Water generally seeps through seams, layer lines, and sometimes through pores in the material itself. If you want to ensure a 3D printed object is watertight (like an outdoor casing for an electronics project or a vase), there are quite a few options available to help with this.

What filament should I use for watertight 3d printing?

ABS, PETG, PLA and PET are good candidates for waterproof 3d prints. ABS in particular can be made waterproof through very easy & quick post-processing with acetone (below).

Polypropelyne, while more expensive and more difficult to print, is an excellent material to waterproof your 3D prints. It is naturally hydrophobic and has a high melting point, which may even allow you to store hot liquids in it.

Avoid using Nylon for any 3d prints that will come into contact with water. Nylon can break down over time in water.

Optimise slicer settings for watertight prints

To maximise your chances of getting a watertight 3d print, adjust your slicer settings to minimise gaps, seams, and other imperfections. This usually means increasing the temperature, decreasing cooling (to allow the material to melt into place and fill all gaps), and increasing your extrusion multiplier or flow multiplier to add more material to help fill gaps. If you’re not using vase mode (“spiralise outer contour”), you’ll want to increase the number of shells – around 5-7 is usually good – as well as the number of floor and roof layers.

Vase Mode

Vase mode can sometimes produce better results due to the lack of seams along the Z axis. If you’re using vase mode, consider using a larger nozzle and a wider line width. With only one outer wall you’ll likely need to apply a waterproof coating to achieve a true watertight seal.

Layer height

Reducing your layer height will also help to ensure watertightness in 3D printed parts, albeit at the cost of print time.

Post-Processing

Post-processing your print to make it watertight usually involves adding a layer of something that is waterproof over the top of something that isn’t waterproof. This could be waterproof paint, plastic dip, or, in the case of ABS, using acetone vapours to smooth a layer of ABS on the outside of the part.

Sanding, priming, and painting with waterproof paint can be effective in enhancing waterproofing.

Design Considerations

When designing your part, consider how well your printer will be able to cope with overhangs, sharp angles, and intricate shapes. These features may result in gaps and therefore spots for water to leak through.

With all of these considerations and techniques to get a watertight 3D print, you should be well on your way to making waterproof enclosures, bottles, vases or anything else!