Vapor Smoothing ABS Prints: Acetone Methods That Actually Work

Vapor smoothing is the closest thing to a cheat code in 3D printing post-processing. A printed ABS part with visible layer lines goes into an acetone vapor bath and comes out looking like it was injection molded. The process dissolves the outer surface of the ABS just enough to merge the layer lines into a smooth, glossy finish. I have been vapor smoothing functional parts and display pieces for about two years now, and the results consistently impress people who cannot believe the parts were 3D printed.

Before we start, a critical clarification: vapor smoothing only works on ABS and ASA filaments. PLA, PETG, TPU, and nylon are not soluble in acetone. If you are primarily a PLA printer, this technique is not for you. But if you are already printing ABS (and if you have followed my ABS printing guide, you should be), vapor smoothing is a powerful finishing technique that requires minimal skill and produces professional results.

Method 1: Cold Vapor (Recommended)

The cold vapor method is safer, more controlled, and what I recommend for almost everyone. You need a sealable container large enough to hold your part (a glass jar, plastic storage bin, or even a large ziplock bag works), paper towels, and acetone from the hardware store. Line the bottom and sides of the container with paper towels, pour enough acetone to thoroughly dampen them without pooling at the bottom, place your part on a raised platform (I use a small piece of aluminum foil crumpled into a stand), seal the container, and wait.

The key to good results is patience and monitoring. Under-smoothing leaves you with reduced but still visible layer lines. Over-smoothing melts fine details, rounds sharp edges, and can cause the surface to drip or sag. Check your part periodically by briefly opening the container (hold your breath, acetone fumes are no joke). When the surface looks uniformly glossy with no visible layer lines, remove the part and let it air-dry in a ventilated area for at least 24 hours before handling.

Method 2: Heated Vapor (Advanced)

Heated vapor smoothing uses a hot plate or electric stove to gently warm a small amount of acetone in a sealed metal container, creating a denser vapor cloud. This method is faster (10-30 minutes for full smoothing) but significantly more dangerous because acetone vapor is extremely flammable. I only recommend this method if you have a well-ventilated workspace, use an electric heat source (never open flame), and have experience handling solvents.

What to Smooth (and What Not To)

Vapor smoothing is excellent for display pieces, cosmetic enclosures, and any part where surface appearance matters. It also slightly improves water resistance by sealing the micro-gaps between layers, which is useful for vases or containers. The process does affect dimensional accuracy, typically adding 0.05-0.15mm to external dimensions as the surface material flows, so do not smooth parts with tight tolerances or press-fit features without accounting for this.

Avoid smoothing parts with fine text, thin walls (under 1.5mm), or mechanical features like gear teeth. The acetone dissolves these details disproportionately fast because they have high surface-area-to-volume ratios. Threaded holes and snap fits should be masked with tape before smoothing if you need them to maintain their geometry. For parts that need both a smooth exterior and precise mechanical features, smooth first and then drill, tap, or cut the mechanical features afterward.

If you are interested in other finishing techniques beyond vapor smoothing, I cover sanding, priming, painting, and other methods in my common mistakes article where I discuss the most frequent post-processing errors. For parts printed in materials that acetone cannot smooth, check my guide on functional prints for design strategies that minimize the need for post-processing entirely.