Insulation - Open Cell

Insulating materials play a major role in comfortable, energy-efficient buildings. Thanks to their heat-insulating effect, they save heating and cooling energy and hence contribute to reducing GHG emissions during operation. In addition, thanks to their sound-insulating effect, they provide the basis for acoustic separation via their density properties. Subsequently, a wide range of products are available for diverse applications and performance properties.

Depending on raw materials, we classify insulation into two broad groups, distinguishing between the inorganic and organic origin of the product. Further subdivision may also be distinguished depending on the further processing of the raw material. Such subdivisions are referred to as either natural or synthetic, with most commercial products being the latter.

As a result of the base raw material of insulation material and the production method, insulating materials exhibit characteristic properties that, in some cases, are not relevant to other materials. Indeed, while insulating materials cover all requirements, no single material perfectly fulfils all requirements, particularly environmental impact requirements. As such, a direct comparison may not always be possible between one product and the next. Nonetheless, to ensure quality in product and application while complying with relevant building codes, insulation products are covered by local and international standards.


Open-cell insulation includes products such as glazing wool and rock wool. With millions of tiny open-cell air pockets forced into products during manufacture, these products allow air migration through their core while restricting heat loss via convection. Also, previously introduced binding agents are activated during manufacture to form a matrix locking the composition together. This process produces the 'spring loading' associated with open-cell insulation, allowing it to regain shape and thickness after compression.

A material will only be able to radiate heat that it can absorb. The glazing strands and their binder agent are poor heat conductors, so heat loss via radiation is negligible.

Dry air is a good insulation gas. So with open cell products, if contamination of the core air by water vapour can be prevented (using vapour permeable membranes), the ultra-small air pockets will significantly limit air movement.

Mineral Wool

Mineral wool is a general term for inorganic fibrous insulating materials like glass wool and rock wool. In all cases, products are formed by spinning or drawing molten minerals and are manufactured in various thicknesses and widths and is often supplied in rolls or slabs.

With a thermal conductivity range between 0.033 – 0.050 W/mK, mineral wool has a good insulating capacity and is open to vapour diffusion to ensure moisture does not build and reduce thermal performance. Even with relatively high moisture levels, they are generally resistant to mould, rot and vermin, representing the default insulation application for roof and wall systems.

Glass wool

Glazing wool varies in colour dependent on the binder mix and is unsuitable in applications where compression loads are likely. Under compression, the air pockets are crushed, reducing thermal performance. Under standard compression loads, however, they are sufficiently firm and stable enough to be used for impact sound insulation.

The primary reason for glass wool's popularity is due to its relatively low thermal conductivity (0.033 – 0.050 W/mK) and low densities (15 – 150 kg/m²). As such, they are easy to manage and, when placed within building envelope systems correctly, do not typically need further fixings.

Low vapour diffusion resistance factors, typically between 1 – 1.3, are a great solution for vapour open building envelopes and a vital component when managing the risk of long-term moisture management.

Rock Wool

Like glazing wool, rock wool is also a popular mineral wool product and has the added benefit of increased fire protection. Without binder agents, rock wool products can withstand temperatures as high as 750 °C, with melting points often over 1000 °C, supplier dependent.

While less flexible in application due to high densities (20 – 200 kg/m²), they are still highly suitable as a thermal control layer. And especially high densities available, combined with high compressive strength, can be used in noise barriers in road building.

From a thermal conductivity standpoint, performance remains in the same range as glazing wool products, between 0.033 – 0.050 W/mK.

Polyester Fibres

Polyester insulation and hydrocarbon compounds-based products are entirely synthetic and can contain recycled plastic fibres or blended with products like wool. Unlike other open-cell products, they contain no binder, flame retardants or other additives.

As a soft and elastic material, polyester products have a course fibrous surface, retaining their contours and form when not under compression. Due to the elastic nature of the material, they do not break during cutting, resulting in no dust that could irritate skin or breathing.

With very low densities (15 – 40 kg/m²), they are sometimes limited in application but retain similar thermal conductivity performance to other open cell products, between 0.035 – 0.050 W/mK.

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