Polystyrene

Polystyrene is a synthetic aromatic hydrocarbon polymer made from the monomer styrene. In construction, it is used in two main forms: Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS). It is a white, rigid foam.

Description of what it is like

• EPS (White): Composed of small fused beads (like a coffee cup). It is slightly permeable to water vapor.
• XPS (Colored): Usually blue, pink, or green. It has a closed-cell structure, making it smoother, denser, and more water-resistant than EPS.
• Both are extremely light (95-98% air).

Origin and where to find it

• Synthetic: Product of the petrochemical industry.
• Raw Materials: Petroleum and natural gas.

Minimum processing required

1. Polymerization: Styrene is polymerized into polystyrene beads.
2. Expansion (EPS): Beads are heated with steam, causing them to expand significantly. They are then molded into blocks.
3. Extrusion (XPS): Polystyrene crystals are melted with additives and a blowing agent, then extruded through a die into sheets.

Tools needed to work on it

• Hot Wire Cutter: The cleanest way to cut it without creating mess (dust/beads).
• Utility Knife/Saw: Can be used but creates static-charged crumbs that stick to everything.
• Adhesive: Must be solvent-free (water-based or specific foams) as solvents dissolve polystyrene.

Common forms of use

• External Wall Insulation (EWI): Boards are glued/pinned to the outside of Brick or Concrete walls, then rendered with Cement.
• Insulated Concrete Forms (ICF): Hollow blocks of polystyrene that are stacked and filled with Concrete.
• Underfloor Insulation: Placed under concrete slabs to prevent cold rising from the ground.

Possible substitutes

• Mineral Wool: Fireproof and breathable (better for timber), whereas polystyrene acts as a vapor barrier.
• Cork: Natural rigid board alternative.
• Polyurethane (PIR/PUR): Higher insulation value per inch, but more expensive.

Limitations and common failures

• Solvents: Dissolves instantly in contact with acetone, gasoline, or solvent-based glues.
• UV Light: Degrades and turns yellow/powdery if left exposed to sunlight for weeks. Must be covered.
• Flammability: It melts and burns, producing thick black smoke. Construction grades usually have fire retardants, but it is still combustible.
• Pests: Ants and mice love to tunnel through it (easy digging, warm).

Risks and safety

• Fire: Significant fire risk if not enclosed behind plasterboard or concrete.
• Toxicity: Burning releases toxic fumes (styrene gas, CO).
• Environment: Non-biodegradable and breaks into microplastics.

Related inventions

• Oil Refinery: Source of raw materials.
• Molding: Process used to shape EPS.

Related materials

• Thermal Insulation: General category.
• Concrete: Often poured into polystyrene forms (ICF).
• Cement Mortar: Used to bond and coat polystyrene boards.
• Brick: Substrate for polystyrene insulation.