Customers often ask whether MJF parts can hold water or air, and it is a fair question for any enclosure that has to protect electronics or carry fluid. The honest answer is that raw nylon is slightly porous, so it is not watertight straight off the machine, but with the right design and a proper sealing step you can absolutely make enclosures that keep moisture firmly out and stand up to daily use outdoors.
We help customers achieve genuinely sealed parts through our MJF & SLS printing service in Perth, from electronics housings that live outdoors to fluid handling components on industrial equipment. Knowing the limits of the raw material up front is the first step to designing a part that seals reliably, and it usually saves a wasted print or two along the way.
Understanding nylon porosity
MJF parts contain a fine network of tiny pores left between the fused powder grains, which is exactly the property that lets dye soak in so evenly and gives such a uniform colour. The downside of that same porosity is that liquids and air can slowly seep through a thin or untreated wall, especially under any sustained pressure or when the part is fully submerged for long periods.
For many enclosures this is simply not an issue, since basic splash resistance is all the part will ever face in normal indoor use. It is only when a part must survive immersion, hold pressure or keep out fine dust over years that the porosity needs to be addressed deliberately with extra steps rather than left to chance.
Design choices that help
Thicker walls leak far less than thin ones, so any structural area that must seal benefits from a little extra material in the design, and around two to three millimetres is a sensible starting point for a sealing wall. Adding a dedicated channel for an O ring or gasket gives a reliable mechanical seal at joints and lids, which is far more dependable than relying on the plastic surface of two mating faces alone.
Smooth, continuous surfaces seal much better than ones broken up by fine detail or texture, so it pays to plan your sealing faces with that in mind and keep logos or part numbers well away from them. A clean, flat mating surface gives any gasket the best possible chance of doing its job, and a captive groove stops the seal wandering out of place during assembly.
Sealing methods that work
When a part genuinely needs to be watertight rather than merely splash resistant, we can apply a sealing process that closes the surface porosity and locks moisture out. Combined with sensible design, this makes truly sealed nylon parts entirely achievable, and the approach you choose depends on whether the part faces splashes, immersion or real pressure in service.
- Impregnation or coating to seal the porous nylon surface.
- O ring or gasket grooves designed in at every joint and lid.
- Thicker walls of two to three millimetres in pressure bearing areas.
- Realistic pressure or immersion testing before deployment.
Testing the finished seal
It is always worth proving a seal rather than assuming it, because a small gap at one corner can undo an otherwise watertight design. A simple submersion test, or a low pressure air test with the part held under water to spot bubbles, quickly shows where any leak path runs and whether the gasket is seating evenly all the way round.
We can run these checks before parts leave the warehouse so you know the enclosure performs the way you need it to. Where a prototype development round makes sense, testing one sealed part first lets us refine wall thickness and groove dimensions before committing to a full batch.
Tell us your sealing needs
Whether you need simple splash resistance or a fully sealed pressure part, tell us the exact conditions it will face in service, including any temperature, dust or chemical exposure. Send your model through a quote and we will design the right sealing approach around it, so the finished enclosure performs reliably for the life of the product.