What will dissolve polystyrene?

What Dissolves Polystyrene?

Polystyrene, the lightweight plastic commonly found in packaging, disposable cups, and insulation materials, isn't easily broken down by most everyday substances. However, one chemical that does dissolve polystyrene effectively is propanone, also known as acetone.

You might recognize acetone as the main ingredient in many nail polish removers. When it comes into contact with polystyrene, acetone breaks down the polymer structure, causing the material to soften, swell, and eventually liquefy. This dramatic reaction happens because acetone molecules penetrate the polystyrene matrix, disrupting the weak intermolecular forces that hold the plastic together. The result? A gooey, almost melted mess—something you’ve likely seen in science demonstrations or viral videos.

While this reaction is fascinating, it’s important to treat acetone with caution. As noted in the CLEAPSS Hazcard HC085A, acetone is highly flammable and an irritant. It should only be used in well-ventilated areas, away from open flames or sparks, and with appropriate protective equipment like gloves and safety goggles. It’s not a substance to experiment with casually, especially around children.

Interestingly, this solubility property is sometimes used in industrial or laboratory settings to bond or shape polystyrene parts. But outside of controlled environments, it’s best to avoid mixing acetone with polystyrene unless you’re fully aware of the risks.

In everyday life, this reaction also serves as a reminder: not all plastics are created equal. Their chemical resistance—or lack thereof—can have real implications for storage, safety, and environmental impact. So while acetone can dissolve polystyrene with surprising ease, respect for the chemical's hazards is just as important as the science behind the spectacle.