Mixing acetone with Styrofoam produces a thick, gooey substance that looks like melting plastic. What’s actually happening is that the acetone dissolves the polystyrene polymer, releasing the trapped air and collapsing the foam’s structure into a dense, sticky mass. A single cup of acetone can dissolve a surprisingly large volume of Styrofoam because the foam itself is 98% air and only 2% actual plastic.
What Happens During the Reaction
Technically, this isn’t a chemical reaction at all. It’s a physical change. The acetone doesn’t break apart the polystyrene molecules. Instead, it seeps into the foam, causes the polymer chains to swell and untangle from each other, and releases all the air that was locked inside. Think of it like dissolving sugar in water: the sugar molecules stay intact, they just separate and disperse into the liquid. The same thing happens here. The long polystyrene chains remain whole, they simply loosen from the rigid foam structure and mix into the acetone.
The process is dramatic to watch. The Styrofoam appears to vanish on contact with the acetone, shrinking rapidly as the trapped air escapes. Because expanded polystyrene is 98% air by volume, the resulting goo takes up a tiny fraction of the original foam’s size. Research has documented volume ratios of roughly 100:1, meaning a large bin of Styrofoam collapses into a small puddle of dissolved plastic. That’s why this demonstration is so visually striking.
What the Resulting Substance Looks Like
The mixture starts as a cloudy, viscous liquid and thickens as you add more Styrofoam. Keep adding foam and it becomes a sticky, putty-like mass with a consistency somewhere between chewing gum and wet clay. If you let the acetone evaporate completely, you’re left with a hard, solid lump of polystyrene. It’s no longer a foam, just dense plastic, because all the air that gave Styrofoam its light, spongy quality is gone for good.
The texture and thickness depend on how much Styrofoam you dissolve relative to the amount of acetone. A small amount of foam in a lot of acetone gives you a thin, syrupy liquid. Packing in as much foam as the acetone can handle produces a thick paste that’s almost too stiff to stir.
DIY Uses for the Mixture
The sticky paste has some genuinely practical applications. Many people use it as a makeshift adhesive or filler. While it’s still wet and pliable, you can spread it into cracks, gaps, or holes where it hardens into solid plastic as the acetone evaporates. It bonds well to wood, concrete, and other porous surfaces.
Common DIY uses include:
- Waterproof sealant: Applied to small roof patches, gutters, or outdoor surfaces where water resistance matters.
- Gap filler: Pressed into cracks in walls, floors, or foundations as a rigid filler that won’t shrink much once cured.
- General-purpose glue: Used to bond materials together, though it’s not as strong or reliable as commercial adhesives.
- 3D printing ink: Researchers have explored using the dissolved mixture as a printing material for direct ink-write 3D printers, offering an affordable way to recycle Styrofoam waste into new objects.
Keep in mind that the hardened result is just polystyrene plastic. It’s rigid but brittle, and it won’t flex or absorb impact the way commercial sealants do. For quick fixes and small projects it works fine, but it’s not a replacement for purpose-built products in structural applications.
Safety Considerations
Acetone is the main hazard here. It evaporates quickly and produces strong fumes that irritate your eyes, nose, throat, and lungs. Breathing moderate to high concentrations can cause headaches, dizziness, and nausea. Skin contact dries out and cracks your skin with repeated exposure. Always do this outdoors or in a very well-ventilated area, and wear gloves if you’re handling the mixture directly.
Acetone is also highly flammable. Keep it far from open flames, sparks, or heat sources. Use glass or metal containers, not plastic ones, since acetone dissolves many types of plastic beyond just polystyrene.
Safer Alternatives to Acetone
If the fumes concern you, d-limonene is a less harsh option. It’s the compound that gives oranges and lemons their citrus scent, and it dissolves polystyrene just as effectively without breaking down the polymer chains. Research in the Journal of Food Science found that limonene could dissolve nearly half a gram of polystyrene per gram of solvent at room temperature. Other natural compounds found in essential oils, including terpinene and cymene, also work well.
D-limonene is considered an eco-friendly solvent and is far less irritating to breathe than acetone, though it still requires ventilation and can irritate skin with prolonged contact. It’s available at most hardware stores as a citrus-based degreaser. The tradeoff is speed: acetone dissolves Styrofoam almost instantly on contact, while limonene works more slowly.