Vapor Smoothing
Also known as: Chemical Vapour Smoothing, Vapour Polishing, PostPro, Solvent Smoothing
Vapor smoothing exposes polymer AM parts to a controlled solvent vapour that briefly reflows the outer surface layer, eliminating the staircase/layer texture and reducing roughness to injection-moulding levels. The vapour condenses on the surface, lowers the local viscosity, and surface tension pulls the molten skin smooth before it re-solidifies. The process is dimensionally near-neutral (typical change <50 µm) and seals the porous surface, improving cleanability and (often) elongation at break.
Why AM parts need this
SLS, MJF, and FDM polymer parts have an open, porous, matte surface (Ra 8–20 µm) that traps contaminants and shows visible layer lines. Vapor smoothing reduces this to Ra <1–2 µm in a single automated cycle, giving an injection-moulding-grade finish without manual sanding. It is the standard route to cosmetic and hygienic (cleanable, watertight) surfaces on production polymer AM parts — medical device housings, ducting, consumer goods, footwear. Unlike mechanical finishing, it reaches recesses and complex surfaces uniformly because the vapour penetrates everywhere the gas can flow.
Achievable surface finish
Typical input Ra
12 µm
Achievable Ra
0.5–1.5 µm
SLS/MJF PA12 as-built Ra 8–15 µm → Ra 0.5–2 µm after smoothing. FDM layer lines are largely eliminated though some waviness from thick layers can remain.
Key parameters
Automated systems (AMT PostPro, DyeMansion Powerfuse S): full cycle including solvent recovery. Throughput scales with chamber size.
Near-neutral — material is reflowed, not removed. Fine sharp edges soften slightly (radius increases a few tens of µm).
Closes surface porosity — parts become cleanable and can hold pressure/liquid. Important for medical and fluidic applications.
Process chemistry is polymer-specific. PA12/PA11 (SLS/MJF) and TPU are the most common. Verify chemistry for each material.
Limitations
- Polymer-only — not applicable to metal AM
- Slightly softens sharp edges and fine features (a few tens of µm radius increase) — not for parts needing crisp micro-detail
- Process chemistry is polymer-specific — incompatible solvent/polymer pairs give poor or no result; test coupons first
- Not a dimensional-correction process — out-of-tolerance parts stay out of tolerance
- Very thin walls can over-soften and distort — validate parameters for wall sections below ~1 mm
Related tools
Providers
AMT (Additive Manufacturing Technologies)
UK developer of PostPro chemical vapour smoothing systems that eliminate layer lines and produce injection-moulding-grade surfaces on polymer AM parts.
Sheffield, GB
PostProcess Technologies
Automated resin support removal and surface finishing for SLA, DLP, PolyJet, and FDM. Software-driven DECI Duo and RADOR systems reduce manual labour in AM post-processing.
Buffalo, NY, US
DyeMansion
German specialist in end-to-end post-processing systems for polymer AM: depowdering, surface finishing, and dyeing in a single automated workflow.
Planegg, DE
Ra and cycle-time ranges from AMT PostPro and DyeMansion published application data (manufacturer tier). Dimensional-change figures from AMT technical literature.
All post-processing