Vapor Smoothing for 3D Printing

Vapor smoothing melts away rough layer lines with vaporized solvents, leaving surfaces so sleek they could pass for injection-molded. This is not just about appearance: it can preserve fine details, ensure the reproducibility of the results, and applicable to various materials, thus enabling your product to perform exceptionally well in terms of cosmetic effects, functionality and durability.

Sleekness redefined for 3D prints
Detail-safe surface perfection
Batch-consistent polish

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Left: Vapor Smoothed/Right: Standard Finish

What Is Vapor Smoothing & How Does It Work?

Vapor smoothing, also called chemical vapor smoothing, vapor polishing, or vapor fusion, is a post-processing technique for enhancing 3D printed parts’ surface finish. It targets flaws like visible layer lines and “sugar cube-like” textures by exposing parts to vaporized solvents, and is widely used for parts from processes such as Multi Jet Fusion (MJF) and Selective Laser Sintering (SLS). By partially melting and dissolving the material surface, it creates a smooth, glossy finish—ideal for cosmetic and functional uses, and valuable in industries like automotive and aerospace where smoothness and precision matter.

Vapor smoothing relies on controlled chemical reactions between vaporized solvents (e.g., acetone, ethanol) and part surfaces. A cleaned part is placed in a sealed chamber with solvent, which is heated to vaporize. The vapor fills the chamber, condenses on the surface, and interacts with the material—melting and smoothing the outer layer (with surface particles’ peaks flowing into valleys to boost smoothness) to eliminate imperfections, resulting in a polished finish. And that is to say, in vapor smoothing, no material is removed like other traditional surface treatments; instead, a controlled chemical melt refines the surface. After processing, the part is dried and cooled, with duration depending on size and complexity, up to several hours.

Improved Surface Finish

Vapor smoothing significantly reduces surface roughness, resulting in a much smoother, more polished appearance. This process enhances the overall aesthetics of 3D printed parts by minimizing visible layer lines and imperfections. Some studies have shown that chemical vapor polishing can increase the surface finish of materials by 800% to 1000%. The smoother surface(with roughness reduced from over 250 μin RA as-printed to 64–100 μin RA or even under 40 μin RA after smoothing) is ideal for applications requiring high-quality visuals, such as consumer products or prototypes.

Retention of Mechanical Properties

Vapor smoothing improves the visual appeal and surface quality without compromising the part’s mechanical strength or functionality. Tests have shown minimal changes in the mechanical properties of parts after smoothing.

Benefits of Chemical Vapor Smoothing

Standard Finished | Vapour Smoothed

Maintain Features & Dimensional Accuracy

Typical dimensional changes are kept within ±0.1%–±0.3% of the original size, ensuring critical details and tolerances remain intact.

Repeatable Processing Results

The process achieves closed-loop operation through controlled parameter settings, ensuring highly consistent results for different batches or identical parts with minimal repeatability errors.

Enhanced Hygiene and Moisture Resistance

Vapor smoothing cuts down on both bacterial growth and the absorption of moisture by reducing porosity, which is a big plus for parts used in settings where cleanliness matters. For example, tests on Nylon 12 parts showed that after vapor smoothing, the growth of MRSA bacteria dropped by 60%. This makes it a strong fit for uses in healthcare or food processing, where keeping things sterile is non-negotiable.

Uniform Coverage for Complex Geometries

Unlike methods that coat surfaces, vapor smoothing can reach every nook and cranny of a part—including hard-to-reach spots or areas you can’t easily see. This means even the most complex designs, with internal features or tight spaces, get a consistent, smooth finish all over. Its a key benefit for parts with intricate shapes that are tough to polish evenly with other techniques.

Considerations Before Vapor Smoothing

Vapor Smoothing Settings

Different vapor smoothing systems and manufacturers utilize unique parameters and solvents for the smoothing process. Key variables that are often adjusted include temperature and pressure settings, with each SLS material requiring a distinct profile to ensure optimal results.

Impact of Part Geometry

The geometry of the part, such as wall thickness and overall size, can influence the vapor smoothing process and should be considered when configuring the smoothing profile. For example, we has different machine profiles for thin Nylon 12 Powder parts (with walls under 2 mm thick) and thicker parts (over 3 mm thick), ensuring the settings are tailored for each design’s specific requirements.

Racking and Attachment Marks

Parts are typically suspended from metal wire racks during the vapor smoothing process, which requires areas to attach wires or clips. Though the marks left by these attachments are minimal, it’s possible to eliminate them by adding a connection point to the design or, for large production runs, linking multiple parts together during the design phase. Tip: the marks left on elastic materials such as TPU will be more prominent.

Solvent Pooling Management

To prevent the accumulation of vapor solvent in concave areas, parts with cup-like features should be positioned facing downwards to promote runoff. In cases where design flexibility allows, it may be beneficial to avoid including such features altogether to optimize the vapor smoothing process.

Consult with Experts

Design Guide for Vapour Smoothing

Material compatibility

Ensure the 3D printed material (e.g., PA-12, ABS) is compatible with the solvent used in vapor smoothing; check material-solvent reactivity to avoid degradation.

For more details, refer to Material Compatibility of Vapor Smoothing (click to navigate)

Maximum Part Size

The maximum size for parts that can be processed is 550mm×350mm×350mm (21.65 in. × 13.78 in. × 13.78 in.). This size allows for a wide range of part designs to be effectively smoothed and finished.

Minimum Feature Size

The smallest feature size that can be effectively vapor smoothed is 0.03 in. (0.762mm). This ensures that even fine details can be processed for smoother finishes.

Tolerances

Well-designed parts typically achieve tolerances of ±0.010 in. (0.25mm) plus 0.1% of the nominal length. Keep in mind that tolerances may vary depending on the geometry of the part, particularly for complex or intricate designs.

Racking/hooking Features

For efficient vapor smoothing, parts should ideally feature through holes with a minimum diameter of 0.04 in. (1mm) or exterior walls measuring 0.04 in. (1mm) to 0.20 in. (5.1mm) to facilitate easy suspension on a rack. Though the process works for nearly all parts, some may require a small sacrificial feature to aid hanging—this is later removed, leaving only a tiny, roughly 2mm non-smooth mark.

Hollow or enclosed features

For hollow parts or enclosed cavities, include small vent holes (minimum 0.02 in. / 0.5mm diameter) to allow solvent vapor circulation and prevent pressure buildup, ensuring even smoothing inside and out.

Wall Thickness

Parts with radiused internal features yield the best results with vapor smoothing, as they help maintain consistency during the process. It is recommended to keep the wall thickness consistent across the part for more uniform smoothing and better aesthetics. The minimum wall thickness should be 0.030 in. (0.762mm) for optimal results.

Warpage

Larger parts (greater than 7 in.) and parts with thin features are more likely to experience warping. To minimize this, we recommend maintaining a uniform thickness of 0.125 in. (3.175mm) to ensure stability throughout the vapor smoothing process.

Overhangs and sharp edges

Avoid extreme overhangs (>45°) or razor-sharp edges, as solvent vapor may cause uneven melting—add radii to sharp corners. (minimum 0.01 in. / 0.25mm radius) for more consistent results.

Post-Process Finishing

Vapor smoothing can be combined with additional finishing steps such as adding tapped or threaded inserts or applying paint. These further enhance the functionality and appearance of the part, making it suitable for a wide variety of applications.

Vapour Smoothing for Health & Safety Industry

Test	Details	Normative Reference
Food Contact Test	KingStar's SLS-printed PA-12 parts, after vapor smoothing, do not pose risks to consumer health or affect food quality.	(EC) 10/2011 Annex V, Chapter 3, Table 3, OM 3, 2 hours at 70°C; DS/EN1186-01:2002; DS/EN1186-03:2002; DS/EN1186-14:2002
Skin Irritation Test	KingStar's SLS-printed PA-12 parts, after vapor smoothing, show no skin-irritating effects.	ISO 10993-10 (2013); ISO 10993-1 (2018); OECD TG 439
Cytotoxicity Test	KingStar's MJF-printed PA-12 parts, after vapor smoothing, produce no cytotoxic effects.	ISO 10993-5 (2009); ISO 10993-1 (2010); ISO 10993-12 (2012)
Microbiological Test on MRSA Bacteria	KingStar's MJF-printed PA-12 parts, after vapor smoothing, reduce MRSA bacterial growth by 99.88%.	MOD ISO 22196: 2011
Microbiological Test on E. coli Bacteria	KingStar's MJF-printed PA-12 parts, after vapor smoothing, reduce E. coli bacterial growth by 99.78%.	MOD ISO 22196: 2011

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Material Compatibility of Vapor Smoothing

Material	Printing Process	Solvent	Cost	Notes
Polyamides (PA11, PA12, etc.)	Powder Bed Fusion (SLS, MJF), FDM	IPA, Formic Acid, etc.	Medium	Carbon/glass fiber-filled variants require controlled processing time to avoid over-etching of reinforcing materials
Acrylonitrile Butadiene Styrene (ABS)	FDM	Acetone, MEK	Low	Highly volatile solvents require strict temperature control and ventilation to prevent excessive part shrinkage.
Acrylonitrile Styrene Acrylate (ASA)	FDM	Acetone, MEK	Low	Yields high surface gloss but may experience UV stability issues with prolonged exposure (but still more stable than ABS)
Thermoplastic Polyurethane (TPU), Thermoplastic Elastomers (TPE)	FDM, SLS	Ethyl Acetate, Cyclohexanone, THF	Medium-High	Elastic materials prone to solvent-induced over-swelling; requires shorter processing time and lower temperature
Polypropylene (PP)	MJF, FDM	Heptane, Hexane	Medium	Non-polar solvents have weak etching effect on PP; extended processing time needed for optimal results
Polycarbonate (PC), PC-ABS Blends	FDM, SLS	Dichloromethane, Chloroform	High	Solvents are highly toxic, requiring specialized equipment and protective measures; PC-ABS blends may show uneven results due to compositional variations
Polyether Ether Ketone (PEEK), Polyether Ketone Ketone (PEKK)	High-Temp FDM, SLS	Specialty Fluorinated Solvents	Very High	Requires matched high-temperature and high-pressure environment; only suitable for industrial-grade equipment; high solvent cost and processing difficulty

Applications of Vapor-Smoothed Parts

Automotive Components

Interior trims (knobs, vent covers) for dust resistance and tactile feel
Sensor housings (sealed surfaces for chemical/heat tolerance)
Custom part prototypes (matching injection-molded aesthetics)

Consumer Goods

Wearable tech casings (sleek, scratch-resistant)
Custom jewelry prototypes (preserved fine details with polished look)
Appliance knobs/covers (fingerprint-resistant, easy to clean)

Aerospace

Lightweight brackets (reduced aerodynamic drag)
Avionics enclosures (moisture/dust protection at high altitudes)
Tooling inserts (enhanced wear resistance)

Medical Devices

Surgical instrument handles (easy sterilization, non-porous)
Patient-specific orthotics (smooth edges to prevent irritation)
Prototype implants (polished finishes for pre-surgical planning)

Cost Example of Vapor Smoothing

Part	Automotive Hose	Eyewear Frames	Rigid Orthotic Insole

Model Dimensions (mm)	180 x 25 x 70	144 x 36 x 47	157 x 23 x 80
Material	TPU 92A Powder	Nylon 12 Powder	Nylon 11 Powder
Quantity	40	80	50
Cost of Vapor Smoothing (per part)	$1.10	$0.49	$0.98
Cost of Sintered Powder (per part)	$4.50	$0.62	$3.98
Total Cost Per Part	$5.60	$1.11	$4.96

*From past projects for a rough reference. The cost of vapor smoothing depends on several variables, including part size, material type, surface complexity, and order quantity. Typically, the cost correlates with the part’s dimensions and quantity, with larger or more intricate parts requiring more processing time and resources.

Frequently Asked Questions

Why should I choose KingStar Mold for vapor smoothing my 3D printed parts?webadmin2025-08-18T05:26:02+00:00

Why should I choose KingStar Mold for vapor smoothing my 3D printed parts?

At KingStar Mold, we stand out with end-to-end expertise and flexibility: As your one-stop manufacturing partner, we handle everything from design consulting (optimizing your parts for vapor smoothing upfront) to 3D printing and post-processing—so you can hand off projects at any stage, whether it’s a concept or finished prints needing refinement.

Our process is dialed in for materials like PA12, ABS, and TPU, using custom solvent blends to preserve even 0.03in details while achieving injection-mold-quality finishes. We accommodate parts up to 21.65×13.78×13.78in with tight tolerances (±0.010in +0.1% of length) and include in-house drying/curing, ensuring consistency from design to final part. Whether you need full production support or just smoothing for existing prints, we adapt to your workflow seamlessly.

How long does the vapor smoothing process take?webadmin2025-08-18T06:11:35+00:00

How long does the vapor smoothing process take?

The duration of the vapor smoothing process typically ranges from several minutes to several hours. It is influenced by factors such as the size and complexity of the part, the material it is made from, and the specific solvent used. Smaller and simpler parts may only take 10 to 30 minutes to complete the vapor smoothing process. For example, some small – scale, single – material parts with simple geometries can be smoothed within this time frame. In contrast, larger or more complex components may require a longer exposure time to ensure that all surfaces are fully smooth. This process may extend to 90 to 120 minutes or even longer.

Furthermore, different materials react differently to solvent vapors. For example, materials like PLA may require a longer exposure time when using less potent solvents (such as ethyl acetate), while common materials like ABS or PA may have a relatively shorter processing time when using the appropriate solvents.

Can vapor smoothing be used for all types of 3D printed parts?webadmin2025-08-18T05:37:49+00:00

Can vapor smoothing be used for all types of 3D printed parts?

No, vapor smoothing isn’t suitable for all 3D printed parts—it depends on the part’s material, geometry, and intended use.

It works best for thermoplastic parts (e.g., PA, ABS, TPU) printed via processes like SLS, FDM, or MJF, as these materials respond to solvent vapors by melting and reflowing to smooth surfaces. However, parts made of non-thermoplastic materials (metals, ceramics, thermoset resins) won’t react with solvents and can’t be smoothed this way.

Additionally, parts with extremely fine features (smaller than 0.03in/0.762mm) or delicate structures may risk distortion or loss of detail if over-exposed to solvents. Similarly, large parts (>7in/178mm) with thin walls are prone to warping, requiring careful design adjustments to be compatible with the process.

That said, with proper design tweaks (e.g., uniform wall thickness, vent holes for hollow parts), most functional thermoplastic parts can be effectively smoothed—we even handle challenging geometries by adding temporary sacrificial features when needed.

How does vapor smoothing compare to other post-processing techniques?webadmin2025-08-18T06:17:43+00:00

How does vapor smoothing compare to other post-processing techniques?

Unlike traditional surface treatment processes, vapor smoothing achieves smoothness by melting and redistributing the material surface, using the raised peaks to compensate for the depressed valleys. In contrast, traditional surface processing smooths the surface by removing the raised peaks, bringing each part to the lowest point of the depressed valleys. Therefore, vapor smoothing has a much smaller impact on the size of the components compared to other traditional methods.

Which 3D printing materials are suitable for vapor smoothing?webadmin2025-08-18T05:07:56+00:00

Which 3D printing materials are suitable for vapor smoothing?

Vapor smoothing works by using solvent vapors to gently melt and smooth a part’s surface—so materials that respond to this controlled melting (thermoplastics) are ideal. These include polyamides (PA11, PA12), ABS, ASA, TPU, TPE, PP, PC, and high-performance options like PEEK/PEKK.

Materials that don’t melt or resist solvents (e.g., metals, ceramics, thermosets like epoxy resins) are unsuitable, as they won’t react with the vapor to achieve a smoothed finish.

How does vapor smoothing affect the mechanical properties of parts?webadmin2025-08-18T05:13:16+00:00

How does vapor smoothing affect the mechanical properties of parts?

Vapor smoothing can impact mechanical properties in moderate to significant ways, depending on the material and application:

It often significantly enhances surface-dependent properties: Reducing surface roughness eliminates stress concentration points, boosting fatigue resistance and impact strength (by minimizing crack initiation). It also seals porous surfaces, improving moisture resistance and airtightness—critical for parts exposed to fluids or humidity.

For bulk properties like tensile strength or flexural modulus, changes are typically minor. The process only affects a thin surface layer (microns to tens of microns), leaving the core material’s integrity and baseline mechanical performance largely intact.

In short, it strengthens surface-reliant functionality without compromising the part’s core structure.

What is vapor smoothing for 3D printed parts and what is the workflow?webadmin2025-08-18T05:21:13+00:00

What is vapor smoothing for 3D printed parts and what is the workflow?

Vapor smoothing is a post-processing technique that refines 3D printed parts by exposing them to vaporized solvents, which gently melt and smooth the surface to eliminate layer lines, roughness, or porosity—think of it like “steam ironing” a wrinkled shirt, but for 3D prints, using controlled vapor to melt the surface, letting peaks flow into the valleys on the micro level to produce a smooth surface without altering the part’s core shape.

The workflow is straightforward: Parts are placed in a sealed chamber, where vaporized solvent (matched to the material) circulates, softening the outer layer. This layer then reflows and solidifies, creating a sleek finish. After processing, residual solvent is vented, leaving a smoothed, functional part. Once the vapor smoothing cycle ends, parts may retain small amounts of residual solvent. A controlled curing phase (often with gentle heating or ambient air circulation) helps evaporate any remaining solvent and allows the surface to fully harden, preventing tackiness or potential deformation. This final step ensures the smoothed surface is durable and directly ready for use.

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