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Polystyrene Insulation vs Mineral Wool

Insulation is critical to any building project, affecting comfort, energy efficiency, and environmental impact. Two of the most popular insulation materials on the market are polystyrene and mineral wool. Each has unique advantages and applications, making choosing between them significant for homeowners, builders, and architects.

What is polystyrene insulation?

Polystyrene insulation is a synthetic aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum. As an insulation material, it is widely used in the construction industry due to its lightweight, durable, and excellent insulation properties. Polystyrene comes in various forms, including sheets and beads, each suited to different applications in building insulation. The two primary types of polystyrene insulation are Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS).

Expanded Polystyrene (EPS)

EPS is characterised by its white appearance and expanding polystyrene beads with steam, causing them to fuse in a mould. This process results in a lightweight, rigid foam with a closed-cell structure. EPS insulation is versatile and can be used in various applications, including wall insulation, roofing, and below-ground applications. It is known for its good thermal insulation properties, resistance to moisture absorption, and cost-effectiveness.

Extruded Polystyrene (XPS)

XPS is typically denser and stronger than EPS due to its manufacturing process, which involves extruding polystyrene through a die after melting with blowing agents. This process yields a foam with a uniform closed-cell structure with high moisture resistance and thermal insulation capability. Depending on the manufacturer, XPS is easily recognised by its often blue, pink, or green colour. Due to its higher compressive strength and better moisture resistance than EPS, XPS is particularly suitable for heavy-duty applications such as below-grade insulation (e.g., basements and foundations) and roofing systems. XPS is integral to our DPC insulation system alongside Mosaic Render and Aquabase.

Polystyrene beads

One unique application of polystyrene is its use as beads for blow-in cavity wall insulation. This method involves drilling small holes into the exterior wall of a building and using specialised equipment to inject the polystyrene beads into the cavity. Once in the cavity, the beads settle, forming a dense, insulating layer that significantly reduces heat transfer through the walls. This technique is particularly effective in retrofitting older buildings with improved insulation without extensive construction work. The beads can also be combined with a binding agent that helps them adhere to each other and the cavity walls, ensuring a stable and durable insulation solution that minimises air leakage and heat loss.

Problems with Cavity
Polystyrene beads being blown into a cavity

Advantages of Polystyrene Insulation

Polystyrene insulation offers several advantages, making it a popular choice among builders and homeowners. Its key benefits include:

  • Excellent Thermal Insulation: Polystyrene provides high resistance to heat flow, helping to maintain consistent indoor temperatures and reduce energy costs.
  • Moisture Resistance: Both EPS and XPS offer good resistance to moisture, with XPS being particularly effective in wet environments.
  • Lightweight and Easy to Install: Polystyrene is light and easy to handle, making installation quick and efficient.
  • Versatility: In sheets, panels, and beads, polystyrene insulation can be used in various applications, from walls and roofs to floors and foundations.
  • Cost-Effective: Polystyrene is generally more affordable than other insulation materials, balancing performance and cost well.

What is mineral wool?

Mineral wool, a broad term encompassing glass wool and stone wool, is an insulation material manufactured from inorganic materials. Glass wool is derived from recycled glass, sand, and other silica materials. In contrast, stone wool is made from volcanic rock, basalt, or industrial waste products that mimic the natural rock’s properties. These raw materials are melted at high temperatures and then spun into fine fibres, creating the base material for mineral wool insulation.

How is it manufactured?
  1. Melting: The first step in manufacturing mineral wool is to melt the raw materials. For glass wool, this involves melting recycled glass and silica sand at temperatures around 1,500°C. For stone wool, basalt rock and other materials are melted at temperatures up to 1,600°C. This process is energy-intensive and requires the use of a furnace.
  2. Fibre Formation: Once the materials are melted, they are spun into fibres. This is achieved by rapidly spinning the molten material and blowing it with a high-velocity air stream or spinning it in a centrifuge equipped with small nozzles. The process forms fine, intertwined fibres with a diameter much thinner than human hair.
  3. Binding and Oil Application: After the fibres are formed, they are coated with a binder and oil to decrease dust and make the fibres water-repellent. The binder helps the fibres stick together, forming a cohesive mat. This step is crucial for creating batts that can be handled, cut, and installed without falling apart.
  4. Curing: The fibrous mat is then passed through an oven and heated to cure the binder, solidifying it into a stable form. The curing process also removes any excess moisture from the batts, ensuring they are dry and ready for use.
  5. Cutting and Packaging: Finally, the cured mineral wool is cut into batts of specific sizes and thicknesses to fit standard construction framing dimensions. The batts are then compressed and packaged for shipping to retailers or construction sites.

mineral wool in insulation systems

Key characteristics

Polystyrene insulation vs mineral wool

Thermal performance

One of the primary functions of insulation is to reduce heat flow, thereby improving a building’s energy efficiency. Polystyrene insulation, particularly XPS, has a higher R-value per inch than mineral wool, providing greater heat flow resistance. This makes polystyrene a better choice for applications where space is limited, as it can achieve the desired insulation level with less thickness.

Fire resistance

When it comes to fire resistance, mineral wool takes the lead. Mineral wool is non-combustible and can withstand temperatures up to 1000°C, making it an excellent barrier against fire spread. While treated with fire retardants, polystyrene can still be flammable and emit toxic smoke when exposed to fire. This makes mineral wool safer in applications where fire safety is paramount.

Environmental impact

Both materials have environmental considerations. Polystyrene is a petroleum-based product, which raises concerns about resource depletion and end-of-life disposal, as it is not biodegradable. However, efforts to recycle polystyrene are increasing. Mineral wool, particularly stone wool, is made from abundant natural resources and contains recycled content, making it more sustainable. However, its production process is energy-intensive due to the high temperatures required to melt the raw materials.

Moisture resistance

Polystyrene, especially XPS, is highly resistant to moisture absorption, making it an excellent choice for below-grade applications such as foundation insulation. While mineral wool does not absorb water easily, it can hold moisture if exposed, reducing its thermal performance and leading to mould growth if not properly managed.

Cost and installation

Cost and installation factors can also influence the choice between polystyrene and mineral wool. Polystyrene is generally easier to install due to its light weight and ability to be cut to fit various spaces. Mineral wool, while heavier, can be easily cut and fitted into irregular spaces without leaving gaps.

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