Learn · Explainer

What is vapor smoothing?

Vapor smoothing (also spelled vapour smoothing) is a chemical finishing process for 3D printed polymer parts. A controlled solvent vapor softens the outer skin of the part, the surface reflows and seals, and the part comes out smooth inside and out. PostPro systems by AMT run it as one automated cycle: Conditioning · processing · curing · drying1.

Test your parts, free See the systems

No cost to evaluate · Parts returned · Typical turnaround 2–3 weeks2

TPU bellows as printed, with a rough gray surfaceAs printed
The same TPU bellows after PostPro vapor smoothing, with a smooth, sealed surfaceVapor smoothed
PhotoThe same 3D printed TPU bellows before and after PostPro vapor smoothing. Not retouched.
Surface roughness
13.42 → 1.18 µm32022
BASF Ultrasint TPU01 · HP MJF
Dimensional change
≤ 0.4%42024
PA12 · voxeljet HSS
Burst pressure
up to +7%52024
PA2200 · SLS
Cycle, SF50 and SF100
1.5–2 h1
Conditioning to drying

01The process

How vapor smoothing works

Definition

Vapor smoothing exposes a thermoplastic part to a controlled solvent vapor, so its outer surface softens, flows and resolidifies as a smooth, sealed skin, while the bulk of the part keeps its shape.

A powder-bed 3D printed part, from HP Multi Jet Fusion or selective laser sintering for example, comes out of the printer with a grainy, porous surface made of partly fused powder. Vapor smoothing does not sand that surface away. It melts the very top of it for a moment so it levels itself, closes the pores and sets again. On a PostPro system that happens in four automated stages:

  1. Conditioning

    Parts are conditioned in the chamber to reach the right processing conditions.

  2. Processing

    Vaporized consumable is injected into the chamber and smooths part surfaces under controlled conditions.

  3. Curing

    The consumable is removed from the surface and the surface resolidifies.

  4. Drying

    Parts are dried so no consumable remains in the chamber, ready for use.1

A full cycle takes 1.5–2 h (SF50, SF100) · 2 h (SFX, SF2X)1. Because the finishing agent reaches the part as a vapor, it acts on every exposed surface at once, including internal channels that no tool can reach.

02The result

What vapor smoothing does to a part

Four things change, and AMT has published measurements for each. Every result below names the material it was measured on; results depend on material, printer and recipe.

  • Surface

    13.42 → 1.18 µm32022

    Surface roughness, as printed to vapor smoothed BASF Ultrasint TPU01 · HP MJF

  • Sealing

    Reduced surface porosity on UL94 V-0 flame-retardant parts6

    Case study HP 3D HR PA 12 FR · HP MJF

  • Strength

    +38.1% (XY)42024

    Elongation at break PA12 · voxeljet HSS

  • Strength

    up to +7%52024

    Burst pressure PA2200 · SLS

  • Dimensions

    ≤ 0.4%42024

    Dimensional change PA12 · voxeljet HSS

  • Dimensions

    ≤ 0.4%52024

    Dimensional change PA2200 · SLS

Why sealing matters

A sealed surface takes up less water, dirt and sweat, and is easier to clean. That is why vapor smoothing turns up on parts that are handled, worn or washed: prostheses, food-processing grippers and automotive seals.7,8,920242023

The water test on the right shows the difference on two TPU bellows printed together: the drop beads on the vapor-smoothed part and soaks into the as-printed one.

TPU and elastomer results · PA12 results

FOOTAGEWater test: a drop beads on the vapor-smoothed bellows (left) and soaks into the as-printed one (right).

03Compatibility

Which printing processes and materials

PostPro vapor smoothing is built for powder-bed and industrial extrusion parts: MJF, SLS, SAF and HSS; FDM ULTEM and Onyx parts on SFX1. On those printers it finishes nylons, elastomers and polypropylene, plus a long list of other thermoplastics.

The finishing agent decides the material list. PostPro Pure runs in every PostPro system; FA326 adds 100+ thermoplastics10 on the SF50 and SF100; FA9202 is the dedicated agent for polypropylene.10 By printing process: MJF · SLS · SAF and HSS · industrial FDM.

04Equipment

Manual vs automated, closed-loop smoothing

Hobbyists smooth ABS prints with acetone vapor in a jar or a heated box. It works on some extrusion plastics, but the operator controls nothing precisely: time, temperature and vapor concentration drift, results vary from part to part, and the solvent vapor escapes into the room.

Industrial vapor smoothing turns that into a controlled machine process. On a PostPro system:

  • SF50 and SF100: Closed-loop system with consumable recovery1; RFID consumable recognition and management1; RFID-controlled access11.
  • SFX desktop system: No external extraction system required11; Quick-change recovery cartridge11.
  • SFX, SF50 and SF100: the cycle runs from a recipe on the touchscreen, not from a stopwatch.11

That is what makes vapor smoothing repeatable enough for production parts. Compare the four PostPro systems.

05Alternatives

Vapor smoothing vs other finishing methods

Abrasive methods such as media finishing, tumbling and sanding remove or flatten material and leave the surface open. Dyeing changes color, not texture. Coatings add a layer that seals as long as it stays intact. Vapor smoothing reflows the part’s own surface, so it smooths and seals in one step, and it is often combined with dyeing.

Vapor smoothing vs sanding, tumbling, dyeing and coating, side by side

06Terms

Vapor smoothing vs vapor polishing

Same principle, different starting part. Vapor polishing is the machine-shop name for reflowing the surface of machined plastic parts, usually to bring back clarity on polycarbonate or acrylic. Vapor smoothing is the name used for 3D printed parts, where the process also seals a porous surface. AMT does both: machined plastics run on the PostPro SF100 with PostPro Pure12.

Vapor polishing for CNC-machined plastics · Not to be confused with vapor honing

07Origins

Who made vapor smoothing industrial

Smoothing plastics with solvents is older than 3D printing. Turning it into an automated, controlled process for industrial 3D printed parts is AMT’s work. Born from University of Sheffield research13: AMT was founded in Sheffield in 2017.

  • The first automated vapor smoothing system for powder-bed 3D printed parts14: the PostPro3D.
  • The largest patent portfolio in vapor smoothing14: 50+15 patents in post-processing technology, among them EP3565712 · GB2582225 · GB2597240B11.
  • The world's largest installed base of automated vapor smoothing systems14: 900+15 PostPro systems installed in 4015 countries.

The patents · The team behind them

08Next

Getting started with vapor smoothing

There are three ways in.

  1. Test your own parts. Send parts to the free benchmark and get them back vapor smoothed with a report: No cost to evaluate · Parts returned · Typical turnaround 2–3 weeks.2
  2. Outsource. The PostPro network has 125+16 production partners in the PostPro network that sell vapor smoothing as a service. Find a partner.
  3. Bring it in-house. Compare the systems, see the list prices and work out your cost per part: systems · prices · ROI calculator.

Questions

Vapor smoothing, explained.

Short answers from AMT’s published specifications and tests. Anything else, ask an engineer.

What is vapor smoothing?

Vapor smoothing finishes 3D printed polymer parts with a controlled solvent vapor. PostPro systems seal and smooth powder-bed 3D printed parts inside and out in one automated cycle with four stages: Conditioning · Processing · Curing · Drying1.

Is vapor smoothing the same as vapor polishing?

They work on the same principle: a controlled vapor reflows the surface of a thermoplastic part. Vapor polishing is the usual name for machined plastic parts, vapor smoothing for 3D printed parts, where it also seals the surface.

Which 3D printing technologies does it work with?

Powder-bed and industrial extrusion parts from MJF, SLS, SAF and HSS; FDM ULTEM and Onyx parts on SFX1.

Which materials can be vapor smoothed?

On the PostPro SF50 and SF100: PA12 · PA11 · TPU · TPE · PP with FA92021,10. With the FA326 agent, the SF50 and SF100 cover 100+ thermoplastics10.

Does vapor smoothing change part dimensions?

Very little. AMT’s published tests measured a dimensional change of ≤ 0.4%42024 on HSS PA12 parts and ≤ 0.4%52024 on SLS PA2200 parts.

How long does vapor smoothing take?

A cycle takes 1.5–2 h1 on the PostPro SF50 and SF100, and 2 h1 on the SFX and SF2X.

Can vapor-smoothed parts be used in contact with food?

For one tested combination, yes: parts printed in FABULOUS DETECT PA11 · PostPro Pure were tested by an independent lab, with Extractables well within regulatory limits under US FDA 21 CFR §177.150017. Other materials and agents need their own testing.

Who invented vapor smoothing for 3D printing?

Solvent smoothing of plastics is older than AMT; automated vapor smoothing for industrial 3D printing started at AMT. The first automated vapor smoothing system for powder-bed 3D printed parts14: AMT’s PostPro3D. The largest patent portfolio in vapor smoothing14, with 50+15 patents in post-processing technology.

Next step

See the price. Run the numbers. Hold the part.

List prices are public and the cost-per-part math is yours to check, with no email needed for either. The free benchmark puts your own parts, vapor smoothed, in your hands.

  1. 01Quote

    Build your quote

    Pick a system and its options and get an itemized total on screen, from AMT’s published list prices.

    Build your quote

  2. 02ROI

    Calculate your ROI

    Compare your cost per part with manual finishing, using your own labor rate and volumes. Every assumption is editable.

    Calculate ROI

  3. 03Benchmark

    Test your parts, free

    Ship us your parts with a prepaid label. We vapor smooth them and send them back with before-and-after photos and a benchmark report.

    Test your parts, free

    No cost to evaluate · Parts returned · Typical turnaround 2–3 weeks2

Prices: AMT list prices, excluding tax and shipping; confirmed in your formal quote.

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