Is PETG Waterproof?

Short answer: the material is waterproof. The print might not be. Those are two separate things, and mixing them up is how people end up with a leaking planter.

The material side

PETG is a polyester, closely related to the plastic drinks bottles are made from. It does not absorb water in any meaningful way, does not soften or swell when wet, and does not rot or corrode. Leave a lump of solid PETG in a bucket for a year and it comes out the same.

It also handles the outdoors reasonably well. It shrugs off rain, resists most household chemicals, and copes with the British climate far better than PLA, which slowly gets brittle outside and softens in the sun. That makes PETG the sensible default for anything that lives outdoors or gets wet — see our material comparison for how it stacks up.

The one weakness is UV. Over a long time in direct sunlight PETG can yellow and grow brittle. If a part will sit in full sun for years, ASA is the better material.

The printing side — where water actually gets in

An FDM print is not a solid lump. It is stacked beads of plastic, and where those beads meet there can be microscopic gaps. Water finds them.

So a PETG print leaks not because PETG absorbs water, but because there is a continuous path of tiny voids from the inside to the outside. Getting a watertight print means closing that path.

How we make a PETG part watertight

• More walls. The biggest lever. Several perimeters mean water has to find a path through several independent beads that line up — far less likely than getting through one or two.
• Thicker top and bottom layers. The floor of a container is often where leaks appear. Extra solid layers seal it.
• Slightly thicker layers, printed hot. PETG welds to itself well when it is properly hot. A slightly larger layer height and a good temperature squash the beads together and reduce voids.
• Dry filament. PETG picks up moisture from the air. Wet filament steams as it prints, leaving little bubbles and pinholes right through the wall. Drying it beforehand matters more for watertightness than almost anything else.
• Orientation. Avoid putting seams and layer starts on the wetted face where possible.
• No sharp internal corners. Water pressure concentrates there.

Done properly, a PETG print holds water at atmospheric pressure — planters, trays, drip catchers, splash guards, outdoor enclosures, boat and campervan fittings. That covers the great majority of what people actually want.

Where PETG prints are not a good fit

Being straight with you:

• Anything pressurised. Compressed air, pumped water, hydraulics. Layer lines are a genuine leak path and, worse, a pressurised plastic part can fail without warning. This is not a job for FDM. Use a moulded or machined part.
• Potable water or long-term food contact. The layer texture holds bacteria in grooves you cannot scrub clean, regardless of the plastic. Fine for a plant pot, not for a drinking vessel.
• Fully submerged, permanently, load-bearing. Possible, but it needs a conversation first.
• Boiling or near-boiling water. PETG softens well before that.

If you need a truly sealed part, the usual route is to print in PETG and add a gasket, an O-ring groove or a bead of silicone at the joint — a design detail that beats fighting the layer lines.

Getting it right

Tell us the part gets wet, and whether it needs to hold water or just survive water. Those need different settings, and it is much cheaper to say so up front than to reprint.

Get an estimate · see the materials we print · browse the print library.