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What is Acoustic Insulation?

Acoustic insulation, sometimes known as soundproofing, is a critical element in the construction and engineering sectors, providing a barrier to unwanted sound. As cities grow and noise pollution becomes more of a concern, the demand for effective acoustic solutions has never been higher. But what are the materials that offer the best acoustic insulation, and how do they compare? In this blog post, we’ll delve into three prominent types of acoustic insulation: Rockwool, Expanded Polystyrene (EPS), and Kingspan K5.

What is acoustic insulation?

Acoustic insulation is a technology designed to mitigate the transfer of sound waves between different areas in a structure. This is achieved by using materials that either absorb, reflect, or dissipate sound waves, thereby reducing noise levels in specific environments. Acoustic insulation plays a vital role in several sectors including residential, commercial, and industrial settings.

Sound travels in the form of waves, and when these waves encounter a material, they can either pass through, get reflected, or be absorbed. Acoustic insulation materials work in one or a combination of the following ways:

  • Absorption: Materials with fibrous or porous structures, like Rockwool, are excellent at absorbing sound waves. These materials transform the energy of the sound wave into heat, thereby minimising sound transmission.
  • Reflection: Some materials, especially those with a dense and solid structure, act as barriers that reflect sound back towards its source. This is commonly seen in materials like concrete walls; however, solely reflective materials are generally not the best choice for sound insulation.
  • Dissipation: Some advanced materials can dissipate sound energy by scattering it in different directions. This is less common in traditional insulation materials but is an area of ongoing research.
Importance and applications

The need for acoustic insulation goes beyond mere comfort and enters the realms of health and productivity. Constant exposure to high noise levels can result in stress, sleep disturbances, and even hearing loss. In industrial settings, effective acoustic insulation is crucial for the safety and well-being of workers.

In residential settings, acoustic insulation can contribute to a more peaceful living environment, protecting inhabitants from street noise, loud neighbours, and internal noises such as plumbing or HVAC systems.

Regulations and standards

Various countries have building codes and standards that dictate the minimum requirements for acoustic insulation. For instance, the UK has regulations for sound insulation between dwellings in the form of Approved Document E of the Building Regulations. These documents specify the minimum STC and NRC ratings for different types of buildings and applications, thereby ensuring a baseline standard for acoustic comfort.


Rockwool is a prominent material in the world of insulation, well-regarded for both its thermal and acoustic properties. Manufactured from natural basalt rock and recycled slag, Rockwool undergoes a melting process at temperatures exceeding 1,500°C, before being spun into fibres to create a wool-like texture.

The unique fibrous structure of Rockwool provides multiple pockets for trapping air, enhancing its insulation capabilities. This structure not only offers excellent thermal insulation but also excels in sound absorption and sound reduction, making it a preferred choice for a variety of acoustic insulation applications.

Noise Reduction Coefficient (NRC)

Rockwool typically exhibits a high NRC rating, often ranging between 0.9 and 1. This means that it can absorb nearly all the sound that strikes it, making it an excellent choice for spaces where sound absorption is crucial, such as home theatres, music studios, and open-plan offices.

Sound Transmission Class (STC)

The STC rating for Rockwool can vary depending on its thickness and the quality of installation. However, it usually falls between 45 to 50. This high STC rating indicates that Rockwool is also very effective at preventing the passage of sound between different areas, making it suitable for partition walls, ceilings, and floors in both residential and commercial settings.


Expanded Polystyrene, commonly known as EPS, is a versatile insulation material widely used in the construction industry. It’s best known for its thermal insulation properties, but it also has applications in acoustic insulation. Composed of pre-expanded polystyrene beads, this lightweight and rigid foam material provides a cost-effective option for various insulation needs.

EPS is made through the polymerisation of styrene, a petrochemical derivative. The resulting material consists of a network of closed cellular pockets filled with air, giving it its unique insulating properties. Because of its closed-cell structure, it’s generally better at thermal insulation than sound insulation. Nevertheless, it does offer moderate acoustic properties and is often used in applications where both thermal and acoustic insulation are required.

Noise Reduction Coefficient (NRC)

EPS typically has a lower NRC rating compared to materials like Rockwool. The NRC rating often falls in the range of 0.7 to 0.8, making it less effective at absorbing sound. However, it’s worth mentioning that EPS can still absorb a fair amount of sound energy and is often adequate for residential and some commercial applications where extreme soundproofing is not required.

Sound Transmission Class (STC)

EPS tends to have a lower STC rating as well, usually ranging from 30 to 40. This makes it less effective than other materials like Rockwool in preventing sound transmission through walls or ceilings. Nonetheless, it still offers a reasonable level of sound insulation that may be suitable for less demanding environments.

Kingspan K5

Kingspan K5 is a specialised form of rigid thermoset phenolic insulation board that has excellent thermal insulating properties. The material typically comes with foil facings and is often used in external wall insulation systems, among other applications.

Kingspan K5 boards are composed of a phenolic foam core, which is a closed-cell structure, generally sandwiched between layers of aluminium foil. The closed-cell foam provides excellent thermal insulation, and the aluminium foil layers add to its thermal and moisture barrier properties.

Noise Reduction Coefficient (NRC)

The NRC rating of Kingspan K5 is generally around 0.7, comparable to that of Expanded Polystyrene (EPS). This suggests that Kingspan K5 is not as effective as Rockwool in absorbing sound. However, it still offers reasonable sound absorption qualities. This makes it suitable for projects where both thermal and acoustic insulation are necessary. As a space-saving option, extreme soundproofing is not the primary concern.

Sound Transmission Class (STC)

Kingspan K5 typically exhibits STC ratings ranging from 40 to 45, which is quite competitive in comparison to other materials like EPS. These numbers indicate that Kingspan K5 is reasonably effective at blocking the transmission of sound between spaces, making it a viable option for partition walls or ceilings in residential and commercial projects.

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