Insulation - Open Cell

Insulating materials are essential for creating comfortable, energy-efficient buildings. By limiting heat transfer, they help reduce heating and cooling energy demands, directly contributing to lower greenhouse gas emissions during operation. Many insulation types also provide effective sound attenuation, thanks to their density and structure, supporting acoustic separation between internal and external spaces.

Material Classifications

Insulation is generally classified by its raw material origin into two main groups:

• Inorganic materials (e.g. mineral-based)

• Organic materials (e.g. petroleum or plant-based)

These can be further divided into natural and synthetic products, with most commercially used insulation falling into the synthetic category.

Each type exhibits unique properties based on its base material and production process. No single insulation material excels in all performance categories—especially environmental impact—so direct comparisons are not always meaningful. Nevertheless, quality and compliance are maintained through local and international standards.

Open-Cell Insulation

Open-cell products, such as glass wool and rock wool, contain millions of tiny air pockets that limit heat transfer via convection while allowing limited air migration. These products also benefit from a 'spring-loaded' structure, enabling them to recover shape after compression.

Dry air is a strong insulator. When protected from water vapour (e.g. with vapour-permeable membranes), the core air in open-cell materials maintains effective insulation. Radiation losses are minimal due to the poor conductivity of the glass fibres and binding agents.

Mineral Wool

Mineral wool is a broad term covering glass wool and rock wool—both manufactured by spinning molten minerals into fibres. Available in various thicknesses and formats (rolls, slabs), these materials offer:

• Thermal conductivity: 0.033 – 0.050 W/m·K

• Good vapour diffusion properties, helping prevent moisture build-up

• Resistance to mould, rot, and pests

They are widely used in roof and wall insulation applications and are known for their reliability and versatility.

Glass Wool

Glass wool varies in colour based on binder composition and is sensitive to compression—crushing air pockets can reduce thermal performance. However, under standard compression loads, it remains dimensionally stable and can also be used for impact sound insulation.

• Thermal conductivity: 0.033 – 0.050 W/m·K

• Density: 15 – 150 kg/m³

• Vapour diffusion resistance (μ-value): 1 – 1.3 Its low density and ease of handling make it an accessible and effective solution, particularly in vapour-open systems.

Rockwool

Rockwool offers added fire resistance, with some products handling temperatures up to 750°C and melting points over 1000°C, depending on supplier and composition. Though generally denser and less flexible, this material is well-suited to high-performance thermal and acoustic applications, including noise barriers and compressed wall systems.

• Thermal conductivity: 0.033 – 0.050 W/m·K

• Density: 20 – 200 kg/m³

Polyester Fibre Insulation

Polyester insulation is a synthetic open-cell material, often incorporating recycled plastic fibres or blended with wool. These products contain no binders, flame retardants, or additives, making them non-toxic and safe to handle.

With a coarse, elastic fibre structure, polyester retains shape without producing dust or particles during cutting—an advantage for occupant and installer health.

• Thermal conductivity: 0.035 – 0.050 W/m·K

• Density: 15 – 40 kg/m³

Due to its soft, low-density form, application is sometimes limited, but it remains a viable option for environments prioritising low irritation and easy installation.