Waterproof 3D Printing Guide: FDM, SLA, and SLS Watertight Enclosure Technologies Compared
Waterproof 3D printing can be used to produce custom or small-batch watertight enclosures, supporting fields such as ocean research, underwater robotics, sustainable engineering, oil and gas, utilities, and defense.
Additively manufactured parts are often considered porous and unable to withstand pressurized environments. However, different 3D printing technologies vary in how materials are bonded, surface porosity, dimensional tolerance, and sealing capability. With the appropriate process selection and proper design of interfaces and O-rings, both SLA and SLS can produce watertight multi-part enclosures.
FDM, SLA, and SLS Waterproof 3D Printing Tests
Formlabs collaborated with the University of Rhode Island's Underwater Robotics and Imaging Laboratory (URIL) to produce multi-part enclosures using Fused Deposition Modeling (FDM), Stereolithography (SLA), and Selective Laser Sintering (SLS), and tested them in an underwater simulated pressure chamber.
The research focused on the watertightness of multi-part enclosures, with test data also covering pressure results, O-ring recommendations, and enclosure design principles. The results showed that with the right printing technology, materials, and sealing design, watertight enclosures required for high-pressure environments can be produced through a simpler and more cost-effective process.
Difference Between Water Resistance and Watertightness
Water Resistance: The ability of a material itself to repel water, or to prevent water from adhering, penetrating, or being absorbed by the material.
Watertightness: The ability of an object or enclosure to prevent water from entering or escaping, primarily dependent on part structure, interfaces, tolerances, seals, and assembly methods.
Therefore, even if the material itself has good water resistance, a multi-part assembly may still leak through seams. Conversely, through precise tolerances, threads, interlocking structures, gaskets, or O-rings, overall watertightness can be effectively improved.
Applications of Watertight 3D Printed Parts
Watertight parts can be applied to boats and outboards, deep-sea robots, underwater photography, sampling equipment, and sensor housings. They can also be used in automotive, chemical research, construction, and utility components that need to transport or contain fluids.
Deployment conditions for ecology, geology, and climate research often change, and commercially available standard equipment may not be suitable. 3D printing can quickly produce customized research tools based on sensors, ports, mounting locations, and operating environments.
NOAA Uses 3D Printing to Produce Waterproof Parts for Coral Research
To study coral reef loss, the National Oceanic and Atmospheric Administration (NOAA) Atlantic Oceanographic and Meteorological Laboratory (AOML) and partner institutions investigate wild corals and recreate specific conditions in controlled environments to study coral responses to rising water temperatures and climate change.
AOML utilizes Formlabs SLA and Fuse Series SLS equipment to produce heavy-duty sampler housings, experimental sensor fixtures, and customized aquarium components. The diverse material options allow researchers to continuously design, iterate, and deploy 3D printed waterproof parts while improving the standardization, accuracy, and comparability of experiments.
"We reduced the cost of our initial sampler design from $1,000 to $220. This means we can now deploy five samplers where we could only deploy one before."
Nate Formel, AOML Researcher
Why Traditional Watertight Parts Are Difficult to Customize
Traditional watertight components are typically made from metal, injection-molded plastic, or rubber. While the unit cost is lower for mass production, modifying connectors, fixtures, and enclosures to meet specific research or equipment needs often incurs higher development costs and longer lead times.
Multi-part enclosures are typically sealed with threads, interlocking structures, O-rings, or gaskets. The compression, diameter, cross-sectional thickness, material, and operating pressure of O-rings all affect the sealing performance, making the selection of appropriate specifications for customized enclosures potentially time-consuming.
Comparison of Waterproof 3D Printing Technologies: FDM, SLA, and SLS
Underwater robotic and mechanical parts often have unique functionalities, and the required size, pressure, materials, and sealing methods vary depending on the project. When choosing a 3D printing technology, a comprehensive assessment should be made of surface porosity, tolerance, interlayer bonding, material properties, post-processing, and anticipated operating pressure.
FDM
Cost is easy to control, but tiny gaps between layers can cause water absorption or leakage, usually requiring process adjustments and post-processing such as coatings.
SLA
Smooth surface, low porosity, and high dimensional accuracy, suitable for producing threaded joints, precise sealing surfaces, and pressure-bearing watertight enclosures.
SLS
Suitable for producing durable and geometrically complex parts; watertightness can also be achieved with correct tolerances, materials, and sealing design.
| Technology | Forming Characteristics | Key Watertightness Considerations | More Suitable Uses |
|---|---|---|---|
| FDM | Molten plastic extruded layer by layer | Tiny gaps may exist between layers, usually requiring process adjustments and post-processing for sealing | Low-pressure prototypes, non-critical enclosures, and verified splash-proof parts |
| SLA | Liquid resin cured and cross-linked layer by layer by light | Low surface porosity, small tolerances, and can withstand higher pressures with seals | Precision enclosures, transparent parts, sensors, and deep-sea research equipment |
| SLS | Laser sintering of part cross-sections in a powder bed | Requires correct material selection, tolerance, and sealing method | Durable functional parts, complex pipelines, fixtures, and small batch parts |
Fused Deposition Modeling (FDM)
FDM extrudes molten thermoplastic material through a nozzle and stacks it layer by layer. Parts typically exhibit anisotropy, meaning mechanical properties change with the direction of force; tiny gaps between layers can also form pathways for moisture infiltration.
Untreated closed FDM parts may not form a reliable pressure seal. In high-pressure environments, the enclosure may crack along the layers or implode. To improve the watertightness of FDM parts, consider:
- Avoiding unnecessary gaps, ports, and openings.
- Increasing wall thickness and shell count, and adjusting extrusion amount and layer height.
- Selecting suitable materials such as PETG or polypropylene.
- Sealing surfaces through sanding, vapor smoothing, resin, or coatings.
- Performing immersion and pressure validation under actual operating pressure.
These methods can improve the watertightness of parts but do not directly guarantee their suitability for high-pressure underwater environments.
Stereolithography (SLA)
SLA cures liquid resin layer by layer with a light source, cross-linking polymer chains within and between adjacent layers. This process creates smooth surfaces with minimal layer lines and low porosity, offering dimensional tolerances suitable for precise assembly.
Multi-part SLA enclosures can be precisely joined using threads or interlocking structures, then combined with O-rings, seals, or gaskets to reduce air gaps. Research tests show that appropriate SLA materials and enclosure designs can withstand high water pressure, but actual capabilities still need to be verified based on material, wall thickness, geometry, and printing conditions.
Selective Laser Sintering (SLS)
SLS sinters part cross-sections in a powder bed with a laser, then spreads new powder and repeats the molding process. SLS parts offer good geometric freedom and durability; with proper design tolerances, surface treatment, and sealing methods, watertight enclosures can also be produced.
Design Tips for 3D Printed Waterproof Enclosures
The watertight capability of an enclosure depends on the material, the part body, and the assembly design. While SLA and SLS can create mating structures with tighter tolerances, for high-pressure environments, it is still recommended to include independent sealing mechanisms such as O-rings.
- Reduce mating surfaces: Minimize the number of parts and potential leakage paths, as permitted by maintenance and assembly requirements.
- Control wall thickness and corners: Avoid excessively thin areas and obvious stress concentrations, and use fillets to improve pressure performance.
- Design stable sealing surfaces: Ensure consistent dimensions and flat surfaces for O-ring grooves, end caps, and enclosure mating surfaces.
- Select materials based on environment: Evaluate the effects of water pressure, temperature, chemicals, UV radiation, and long-term immersion.
- Perform actual testing: Waterproof does not mean pressure-proof; verification should be done under anticipated operating conditions and with a safety factor.
URIL Deep Sea Enclosure Design
URIL is dedicated to lowering the equipment barrier for deep-sea research. SLA equipment like the Form 3+ and the large-format Form 3L allows research teams to design precise deep-sea exploration tools and share open-source designs with research communities that previously lacked resources for underwater data collection.
Research topics include the DEEPi deep-sea imaging and control system, passive stabilization techniques in offshore mobile vessels, and biomimetic pressure-resistant enclosures based on the geometry of nautilus shells.
Biomimetic Pressure-Resistant Enclosures
The research team explored how nautilus shells maintain their structure in high-pressure deep-sea environments through scanning and digital reconstruction. The study compared complex biomimetic geometries with traditional pressure-resistant structures such as spheres and cylinders to evaluate their potential as deep-sea robot enclosures.
How to Choose O-rings for 3D Printed Waterproof Enclosures
URIL tested both face-seal and bore-seal O-rings and preferred face-seal as the enclosure design method. After determining the inner and outer diameters of the housing, the appropriate size can be selected based on the inner diameter, allowing the O-ring to fit snugly against the mating surfaces of the end cap and housing.
In research tests, a "double dash" size O-ring with a cross-sectional width of approximately ⅛ inch (0.139 inches) provided a reliable seal for SLA printed parts. Actual designs should still specify O-ring material, compression ratio, groove size, operating temperature, and pressure.
Waterproof 3D Printing Pressure Test Results
The study produced test enclosures using FDM, SLA, and SLS. Nylon 12 GF powder was printed with a Fuse 1+ 30W SLS machine; Grey Resin, Clear Resin, BioMed Amber Resin, and Rigid 10K Resin were made with a Form 3+ SLA machine.
FDM parts made with PLA filament on a Craftbot machine absorbed water immediately after immersion and therefore did not proceed to subsequent pressure testing.
Tests showed that both SLA and SLS, when combined with O-ring seals, can effectively produce watertight enclosures, with SLA samples performing particularly well overall. Some tested parts withstood pressures equivalent to approximately 4,000 meters below sea level.
More rigid SLA materials performed better in this pressure test, and appropriate post-processing such as sandblasting could also improve performance by reducing surface porosity. The above data are specific to the tested materials, geometries, and test conditions, and should not be directly considered as guaranteed pressure resistance values for other parts.
Conclusion on Waterproof 3D Printing Technology Selection
| Requirement | Recommended Approach |
|---|---|
| Precision, high-pressure watertight enclosures | Prioritize SLA, rigid materials, precise mating surfaces, and O-ring seals |
| Durable and geometrically complex functional parts | Evaluate SLS materials, tolerances, surface treatment, and independent sealing structures |
| Low-cost prototypes or low-pressure applications | FDM can be used for initial verification, but interlayer leakage must be addressed and actual testing performed |
| Deep-sea or safety-critical applications | Conduct full engineering validation based on anticipated pressure, material aging, and safety factors |
Whether a waterproof enclosure functions reliably cannot be determined solely by the printing technology. Material, wall thickness, geometry, printing orientation, post-curing, surface treatment, O-ring design, and assembly quality all affect the final watertightness and pressure resistance.
Evaluate 3D Printing Solutions
If you need to produce sensor components, custom research equipment, or other functional parts, 3DMart can assist in evaluating Formlabs 3D printing equipment, materials, sample testing, and process applications.
Contact 3DMart to evaluate waterproof 3D printing applications