Is Celotex Insulation Soundproof?

Celotex is a popular thermal insulation product used in construction. Its performance, ease of installation, and flexibility make it one of the most popular insulation materials. So how effective is it for soundproofing walls?

Celotex is not good for soundproofing. The material and structure of this product mean that it cannot effectively absorb sound. Although better than having no insulation at all, there are many other products and techniques that have better sound absorption properties.

Celotex is not good for soundproofing. The material and structure of this product mean that it cannot effectively absorb sound. Although better than having no insulation at all, there are many other products and techniques that have better sound absorption properties.

In this article, I will look further into the difference between sound and thermal insulation, how Celotex performs in this area, and a few effective ways to effectively soundproof walls. Let’s get started!

Check out: The 10 Best Soundproofing Materials

The Technical Information of Celotex

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Celotex is a rigid insulation board made of a synthetic material called polyisocyanurate. It is used regularly in construction because of its excellent thermal insulation properties.

Celotex boards are manufactured to fit within cavity walls and joists and are easy to cut to shape, making them easy to install. They also are known for their high performance in high humidity and resistance to fire.

The high thermal performance of Celotex results from the process of trapping gasses within the plastic structure of the board during manufacture, which results in a high level of thermal insulation.

The Difference between Thermal and Sound Insulation

The structure of Celotex is good at trapping heat because to stop heat energy from moving through a wall, it needs to be firm but not completely solid. This creates a barrier that slows the movement of the heat from the warm to the cold side of the wall.

All good thermal insulation will have similar properties, reducing heat transfer by minimizing the solid surface through which heat can transfer.

However, sound insulation works differently. It reduces the sound energy traveling through the wall by absorbing the sound waves affecting it. In this way, sound insulation is similar to thermal insulation in that it blocks energy passing through.

The key difference between the two is that sound insulation needs to be denser than thermal insulation to block soundwaves.

Is Celotex Good for Soundproofing?

Celotex is not good for soundproofing. Although having Celotex within your wall cavity will have more effect on reducing the impact of sound waves than no insulation at all, it does not have enough mass to reduce noise effectively.

To provide effective soundproofing, the best solution is to look at dedicated products manufactured to provide sound insulation. However, you may get better results from other thermal insulation products with better sound insulation.

What Thermal Insulation Can Be Used for Sound Insulation?

A thermal insulation product that is used often for sound insulation is mineral wool. While it is not as effective as dedicated soundproofing products, it is more effective than Celotex due to being a denser material.

Mineral wool, however, does not have the same high performance in thermal insulation as Celotex and is more difficult to install due to being a soft fiber rather than a rigid board. 

There are a few key differences between thermal insulation and soundproofing that we will discuss below.

Principles of Soundproofing

If your goal is to soundproof your wall, then dedicated soundproofing techniques are the best way to reduce noise.

Effective soundproofing will mostly depend on your budget and the amount of noise you want to block. Reducing street noise will require less work than blocking the noise of live music, for example.

Soundproofing should also have multiple layers with different materials to work very well. This is because sound waves travel at different frequencies, resulting in different soundwave lengths, which are all absorbed slightly differently.

The basic principles of soundproofing are:

  • Adding mass
  • Increasing sound absorption
  • Reducing gaps
  • Separating wall layers

I will look into these in some more detail here.

Adding Mass

As discussed previously, denser surfaces are more likely to absorb sound waves, so adding mass to the wall is a good way of absorbing sound. A common product for this is Mass-Loaded Vinyl, but even extra layers of drywall can be used.

Increasing Sound Absorption

Increasing the use of materials that absorb sound both inside and outside the wall will work well alongside a general increase in mass. As discussed previously, mineral wool is one of the more effective types of thermal insulation that also absorbs more sound.

An expensive option would be dedicated sound insulating foam panels installed around the walls and ceilings, but this is primarily for professional situations such as recording studios.

A simple DIY option for sound absorption is to hang rugs, blankets, or other heavy fabrics around walls. While not as effective as real soundproofing construction, this is often used as a cheap, simple method of soundproofing.

Reducing Gaps

Windows and doors allow more sound to transfer through them than walls. Using acoustically insulating curtains or shutters will help to reduce this.

Consider your glazing as well. Double-glazed windows are more effective at reducing noise than single-glazed windows.

Separating Wall Layers

Although not always possible, having a cavity between two solid walls is the best way to reduce general noise in buildings. This will be more expensive, but if you are considering soundproofing in new construction, this will be the most effective option.

You can also build internal walls in existing rooms if you want to minimize sound intrusion, but this will affect the structure and space available and will only be necessary when dedicated soundproofed space is required.


Celotex is a common construction material with excellent properties for keeping heat within your walls, but it does not perform well for sound insulation.

Mineral wool is another thermal insulator that has sound insulating properties, but for the best results for soundproofing, remember these key principles:

  • Add mass to your walls with extra layers.
  • Use absorption through panels or internal insulation to reduce the transfer of sound.
  • Look at ways to reduce the impact of gaps in your rooms.
  • If possible, consider having separate internal and external walls to minimize sound transfer between inside and outside.

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