Testing waterproofing for FDM parts with pressure abuse

waterproofing FDM – Because FDM prints are full of tiny layer gaps, they’re rarely truly air- or water-tight. One maker decided to compare a range of waterproofing approaches head-to-head—coatings inside and out, foam ideas, and even a few unexpected material combinations—using a

Layer lines are already an eyesore on many FDM prints. But when the goal is keeping water out—or keeping it in—those microscopic gaps between layers become the real problem. If you’ve ever tried to waterproof a part made on an FDM machine. you already know the frustration: nothing feels “sealed” for long. and it’s hard to tell which fixes actually work without going through expensive trial and error.

That’s exactly why Half-Baked-Research took a blunt approach: instead of picking one method and hoping, he pitted a bunch of different waterproofing ideas against each other.

The tested options covered both the obvious and the improvised. There were coatings applied either inside the part or on the outside. There was also foam-based waterproofing—an approach he previously tried—along with several community-suggested alternatives intended to prevent parts from getting waterlogged.

To test them in a way that actually represents real pressure. the creator explained that water pressure at a depth of about 10 meters would be enough. Instead of chasing that depth in a pool or natural body of water. the setup used compressed air to ramp up the pressure of what is basically a big bucket of water.

For the pressure chamber, a Vevor vacuum chamber was modified to hold 1 bar (103 kPa) of pressure. That wasn’t plug-and-play. The test required a CNCed metal top plate to make it work.

Not every sample followed the standard script, either. Alongside printed and treated samples, there were wild cards: a PETG cube with a TPU printed cover, a PU molded part, and PETG with thicker walls.

The testing didn’t stop at soaking. In addition to long soak exposure, there were percussive tests intended to see how physical impacts affected water intrusion resistance. After all of that—coatings, variants, and repeated abuse—three approaches came out on top.

Internal epoxy coating and two types of internal PU coating were the winners. Epoxy was the clear leader after repeated abuse, holding up best even when the part was pushed harder than a “gentle water exposure” scenario.

PU rubber, however, earned a thumbs-up for a different kind of need. If you don’t require the highest pressure resistance but you care more about resisting physical abuse, PU rubber is positioned as the practical alternative.

For anyone who’s struggled to make FDM parts behave like true housings—waterproof enclosures, covers, or anything expected to survive contact with wet conditions—this is a rare head-to-head look. It doesn’t just suggest what might work. It shows what survives when the testing gets uncomfortable.

FDM waterproofing 3D printing coatings epoxy coating polyurethane coating PU rubber TPU cover PETG pressure testing layer gaps water intrusion