October 20, 2026 · DIY & Workshop · 6 min read

Homemade Glue from Polystyrene and Petrol: How It Works (and How to Make It Safely)

Drop a piece of expanded polystyrene foam into a jar of petrol and something almost magical happens: the foam collapses like a snowman in the sun, hisses out its air, and disappears into the liquid. Do it with enough foam and you end up with a thick, sticky syrup that — once the petrol evaporates — bonds foam, wood, cardboard and more with surprising strength. It's the same trick model makers have used for decades, sold in shops as "polystyrene cement". Here's the science, the method, and — because this is genuinely a fire-and-fumes hazard — the safety rules to follow before you try it.

Why foam dissolves in petrol

Polystyrene is a plastic built from long polymer chains — think of tangled spaghetti strands packed tightly together. Expanded polystyrene (EPS) is the same material puffed up with air: about 95% of its volume is gas, which is why a fistful of packaging foam vanishes into almost nothing.

Petrol is a cocktail of hydrocarbon solvents, including aromatics like toluene and xylene. Chemists sum it up as "like dissolves like": the aromatic hydrocarbons slide between the tangled polystyrene chains, and the polymer untangles and disperses into the liquid. The foam doesn't melt — it dissolves, releasing its trapped air as it goes, which is why it fizzes down so dramatically.

What you've made is a concentrated solution of polystyrene. Paint it onto a surface and the solvent evaporates, leaving the polymer chains to knit back together — except now they're entangled with the microscopic texture of whatever you pressed them against. That's a solvent weld, and it's exactly how commercial model glue works. The only difference is that shop-bought polystyrene cement uses purer, faster solvents.

What you'll need

• Clean, dry expanded polystyrene — packaging foam or insulation offcuts, torn into fingernail-sized crumbs. Don't use foam that held food or was painted.
• A small quantity of ordinary unleaded petrol (250–500 mL is plenty).
• A wide-mouth glass jar with an airtight lid — metal lid preferred.
• A long stirrer you don't care about, plus nitrile gloves and safety glasses.
• A funnel and an old fine sieve, for straining later.
• A scrap of the material you plan to bond, for testing.

Step by step

1. Set up outside. Choose a still day on open ground or a non-flammable workbench far from buildings, vents and any ignition source.
2. Pour the petrol. Fill the jar about a third full. Keep the lid within reach so you can close it between steps.
3. Add crumbs gradually. Drop in a handful of foam at a time. Each batch will collapse and dissolve; stir gently and wait for it to disappear before adding more. Smaller pieces dissolve much faster.
4. Stop at syrup thickness. Aim for something like warm honey or runny jam. Remember the mix thickens further overnight as trapped air escapes, so err on the thin side.
5. Rest and adjust. Close the jar and leave it for a few hours (or overnight). Too thick? Add a splash of petrol. Too thin? Dissolve more foam. There's no exact recipe — a rough starting point is about 1 part foam to 4–5 parts petrol by volume, but appearance beats arithmetic here.
6. Strain (optional). Pour through the sieve into a second jar to catch paper labels, grit and undissolved lumps.
7. Test on scrap first. Brush a thin coat on both surfaces, press them together firmly for 30–60 seconds, and let the joint sit overnight before trusting it with anything real.

Getting the consistency right

Cured joints feel rubbery-hard and are ready to handle in about an hour, reaching full strength after roughly 24 hours. Thin coats bond better than thick ones — a heavy layer traps solvent underneath and stays soft for days.

Where it shines — and where it doesn't

This glue is excellent at bonding polystyrene to polystyrene, gluing foam sheet to cardboard or wood, sealing saw-cut foam edges, and general low-stress modelling jobs. Because the solvent slightly melts the foam surface, the joint is a weld, not just a stick — pulling it apart usually tears the foam, not the glue line.

Know its limits before you rely on it:

• It's not structural — fine for foam scenery and props, wrong for anything load-bearing or safety-critical.
• It dissolves paint, varnish and vulnerable plastics like ABS and acrylic — test every new surface.
• The bond is fairly brittle and hates peeling forces; joints under flexing will creep apart.
• Long-term water, heat and sunlight degrade it. Never use it on anything hot, anything that touches food or drinking water, or aquarium equipment.

Storage and clean-up

Keep the jar sealed and clearly labelled ("GLUE — POISON — FLAMMABLE"), stored cool and dark, out of the living space and away from children. Make small batches and use them up — solvent gradually escapes even through a good seal, and the glue skins over and thickens in the jar.

For leftovers, don't improvise. Never pour petrochemical waste down a drain or onto the ground, and never burn it. Let the last dribble of glue harden completely in an open outdoor spot (well away from flames — on soil, the residual solvent dissipates quickly), then bin the solid lump as general waste, or hand sealed containers of wet sludge to your local household hazardous-waste collection. Clean brushes with a little petrol, letting the dirty solvent evaporate outdoors in a shallow tray before disposing of the residue the same way.

Repairing foam insulation or scenery for a room makeover? Our guide to calculating how many tiles you need pairs well with the same careful-measure mindset.