Is PLA Waterproof? What Water Actually Does to PLA+ Prints

The short answer

PLA is water resistant, not waterproof. The polymer itself is effectively insoluble in water — reference data lists its solubility in water as 0 mg/ml — so a printed part shrugs off rain, splashes and a damp pocket. What it will not do is seal: fused-filament prints are porous along the layer lines, and PLA softens near 60 °C.

Is PLA waterproof or just water resistant?

The words get used interchangeably, and that is where most confusion starts. Four different properties hide inside "waterproof":

The Formlabs white paper on watertight 3D printing draws the same line: waterproofness is a material's inherent ability to resist absorbing water, while watertightness is an object's ability to stop water entering an enclosure. PLA scores well on the first and needs help on the second.

is pla waterproof — Person wearing yellow rain gear and holding a watering can by the lake

Photo: Thirdman / Pexels

So the honest answer to "is PLA waterproof?" is: the plastic is water resistant, the print usually is not watertight. A keychain that gets rained on is fine. A hollow PLA vessel holding water for a week is not, unless it was printed specifically for that.

Does PLA dissolve or absorb water?

PLA does not dissolve in water. Published reference data for polylactic acid gives a water solubility of 0 mg/ml, a density of 1,210–1,430 kg/m³ and a melting point of 150–160 °C. Drop a PLA+ tag in a bucket and it will still be a tag tomorrow, next month, and next year.

Absorption is a different question, and the answer is "a little". A 2021 study in Polymers immersed FFF-printed PLA and PETG samples in distilled water, salt water and sugar solutions for weeks, weighing and measuring them weekly. Two findings matter here: absorption stabilised after a small number of weeks in both materials, and degradation was noticeably more pronounced in PLA because of its organic nature.

That slow degradation is hydrolysis. Water molecules attack the ester bonds in the polymer chain, and the reaction speeds up sharply with heat. At room temperature the effect is measured in years; in hot water it is measured in hours. This is why a PLA part that has sat in a hot car or a dishwasher does not just look tired — it goes chalky and snaps at the layer lines.

Why do 3D printed PLA parts leak?

Because fused-filament printing builds an object out of beads, not out of a solid block.

is pla waterproof — Abstract image of transparent plastic with water droplets. High contrast and cool tones enhance the texture

Photo: Pexels User Kristina / Pexels

Each layer is a rounded bead pressed onto the one below. Where a bead meets its neighbour, there is a valley; where the nozzle lifts for a travel move, there is a seam. Infill is deliberately partial — typically 10–20% — so the inside of a print is mostly air. Water does not need a hole to get in. It needs a path, and a wall built from four or five stacked beads has plenty of microscopic ones.

The practical consequences:

• Thin walls leak first. Two perimeters at 0.4 mm give a 0.8 mm wall with a porous core.
• The Z-seam is the weakest line. It is a vertical scar where each layer starts and stops.
• Low infill traps water. Once water enters, a 15% infill acts like a sponge and holds it against the walls.
• Shape matters. A flat keychain has almost no volume to fill; a vase or a box does.

How do you make a PLA print watertight?

If the part genuinely has to hold water, the settings matter more than the filament brand. These are the changes that move the needle, in order of impact:

1. Use 4–5 perimeters. Wall count is the single biggest factor. Three walls is a decoration; five walls is a barrier.
2. Drop to 0.12–0.16 mm layers. Thinner layers squash the bead flatter, closing the valleys between layers.
3. Raise the extrusion multiplier by 3–5%. Slightly over-extruding fills gaps that the slicer's maths leaves open.
4. Print at the top of the temperature window. For PLA+ that means 215–220 °C, so each layer fuses into the last instead of sitting on it.
5. Use at least 5 top and bottom solid layers. The floor and lid of a container are where pinholes show up first.
6. Slow the outer wall to 30–40 mm/s. Faster walls cool before they bond.
7. Coat it if it must be reliable. A thin two-part epoxy or a clear polyurethane lacquer seals the surface and the seam. It also hides layer lines.

None of this makes PLA into a plumbing material. It makes a small part hold water at room temperature, which is usually the actual requirement.

Is PLA+ more waterproof than PLA?

No — and this is worth stating plainly because the "+" suggests otherwise.

is pla waterproof — A vibrant collection of rubber rain boots in various colors neatly arranged on a shelf

Photo: Jan van der Wolf / Pexels

PLA+ is PLA with additives that improve toughness and layer bonding. It is not a different polymer, and its water behaviour is essentially the same as standard PLA. The one indirect benefit is that better layer adhesion means fewer open paths between beads, so a PLA+ print is marginally less likely to weep than a badly bonded PLA print.

Where PLA+ genuinely earns its place is in parts that get handled, dropped and pocketed. Nuho India prints keychains in PLA+ at around 215 °C, fusing the letters to a continuous backing plate rather than gluing brittle cut-outs on top. A 14–18 g tag with no glued joint has nowhere for water to sit and nothing to delaminate.

What does Indian weather do to a PLA+ keychain?

Rain is not the problem. Heat is.

A keychain on a bike ring gets rained on, dried by engine heat and morning sun, then rained on again. PLA+ handles that cycle well: it does not swell like laser-cut wood, it does not rust, and it does not scuff like cast metal. What it cannot do is sit in direct sun on a dashboard at 65 °C, where it will creep out of shape under its own weight.

Humidity matters more before printing than after. Coimbatore's monsoon air sits above 80% relative humidity for weeks, and filament left on an open spool picks up moisture that turns into steam at the nozzle — popping, stringing, and weak layers that fail later. The guide to drying filament in Indian humidity covers storage boxes and silica in detail.

For anything that lives outdoors permanently, the constraint is not water at all — it is sun and heat. That is a different material conversation, covered in the notes on 3D printed house name plates and weather.

Does PLA survive hot water, a dishwasher or a hot car?

No, and the reason is a single number. Published glass transition figures for PLA sit around 60–65 °C. Above that, the polymer stops behaving like a rigid solid and starts to creep.

So: rain, yes. A wet bike seat, yes. A dishwasher, never. A dashboard, never.

How can you test whether a print is actually waterproof?

You do not need a pressure chamber. A kitchen scale and 24 hours will tell you most of what you need:

1. Weigh the dry part on a scale that reads 0.01 g.
2. Submerge it in room-temperature water for 24 hours, weighted so it stays under.
3. Pat the surface dry and weigh again.
4. Compare two prints rather than trusting an absolute number. A small gain of a few tenths of a percent is normal for PLA; a gain approaching 1% means water is inside the walls, not just on them.
5. For a container, fill it, stand it on a paper towel and check for a damp ring after an hour.

A part that fails the fill test can still be perfectly fine as a keychain. The test tells you which object you have.

When is PLA the wrong material for water?

If the part is immersed for hours at a time, holds hot liquid, or lives outdoors in the sun, choose something else. PETG tolerates water and impact better; ASA handles UV; polypropylene handles chemicals. The trade-off is detail — PLA+ prints sharper letterforms and finer edges than any of them, which is why it remains the right choice for name tags, number plates and decorative work. The PLA vs PETG durability comparison sets out where each one wins.

The verdict for keychains, tags and desk pieces

For the objects most people actually order — a custom keychain with a name, a number plate tag, a desk name plate — water is a non-issue. These parts are 14–18 g of solid PLA+, printed at 215 °C with letters fused into the backing plate, and they dry in minutes after a soaking.

The rules that matter are simple. Keep them out of the dishwasher. Do not leave them on a dashboard in May. And if a part must genuinely hold water, print it with five walls, thin layers and a coat of epoxy — or print it in PETG and accept slightly softer detail.

Prices and material specs change, and every filament brand publishes its own numbers. Verify against your spool's data sheet before committing a large batch.