Isover vs Rockwool

Thermal performance

There are two things to bear in mind when it comes to thermal performance: thermal drift and the purpose of insulating.

Both brands have a good thermal conductivity rating:

• Isover thermal conductivity: typically 0.032–0.044 W/mK
• Rockwool thermal conductivity: typically 0.035–0.040 W/mK

On paper, Isover would appear to have a slightly better thermal performance per millimetre of thickness; however, when you consider thermal drift, Rockwool performs better.

Why are you insulating your home?

This is an important question to ask yourself as the answer will help you know what products you need to buy.

The main reason people insulate their homes is to improve thermal performance; however, there are other reasons, which both Isover and Rockwool lend themselves better to, such as acoustic performance or fire resistance.

If you’re insulating your home just for thermal performance, it would be wiser to use a different brand with a better thermal conductivity rating, as that would allow you to achieve target U-values with much thinner boards. Some of these include:

• Celotex insulation (thermal conductivity up to 0.022W/mK)
• Ecotherm insulation (thermal conductivity up to 0.22W/mK)
• Kingspan insulation (thermal conductivity up to 0.019W/mK)
• Recticel insulation (thermal conductivity up to 0.022W/mK)

*For reference, these are previous thermal conductivity ratings:

• Isover: typically 0.032–0.044 W/mK
• Rockwool: typically 0.035–0.040 W/mK

Moisture performance

Rockwool is the superior choice for moisture resistance. This is because it’s made from stone fibres, which are hydrophobic, meaning they repel water. It’s also vapour-permeable, meaning trapped moisture can escape instead of accumulating inside the structure, making it highly effective in humid environments like basements, external walls, or flat roofs.

Isover, on the other hand, doesn’t handle moisture well. This is because it’s made from fibreglass, which absorbs moisture easily. Once the insulation gets soggy, it will likely lose all of its thermal properties, as well as lead to mildew and rot.

Acoustic performance

Both brands perform exceptionally well for soundproofing; however, Rockwool has the edge.

Rockwool, being made from stone wool, has a dense and fibrous structure, which makes it exceptional at absorbing sound waves. This results in a dramatic reduction in both airborne noise (voices, music) and impact noise (footsteps, vibrations),and is commonly used in recording studios, apartment blocks, and internal partitions.

Compared to Rockwool, Isover does offer a strong acoustic performance. The flexible and lightweight structure of the insulation effectively reduces noise transmission in stud walls, ceilings, and floors. This is often more than enough for residential applications; however, in high-demand environments, Rockwool is the better option.

Installation

Rockwool

Rockwool is considered less itchy to install than Isover; however, it’s still important to wear protective gear such as gloves, a mask, and long sleeves to prevent loose fibres from contacting your skin, eyes, or lungs.

Because Rockwool is slightly heavier and more dense, installation can be a bit more labour-intensive, but it’s often easier to get a snug, professional fit.

It’s supplied in semi-rigid slabs that can be friction-fitted tightly between studs or joists without the need for staples or netting. These hold their shape well, cut cleanly with a serrated knife, and are less likely to slump or leave gaps over time.

Isover 

Installing Isover is relatively straightforward, coming in lightweight rolls or batts that are easy to cut with a utility knife and fit between joists or studs.

Where it differs from Rockwool is that the material is soft and compressible, which means it will require stapling or otherwise supporting to prevent sagging in walls and ceilings.

Additionally, Isover is made from fibreglass, which is why it’s incredibly important to wear protective equipment, as loose glass fibres can easily cause skin irritation if exposed.

Which is right for me?

As mentioned at the start, the choice between the two comes down to what you’re insulating and why you’re insulating it.

Rockwool is the right choice for those wanting the best acoustic performance possible, indestructible fire-resistance, and a structure that holds form over time (especially if exposed to damp or installed in walls, basements or floors).

Isover is the right choice for those looking to save as much money as possible and need a quick, reliable solution in the short term.

If you need any help with your insulation project, please don’t hesitate to get in touch with us today. We’re proud to be a family-run business and have extensive knowledge in both insulation and flat roofing.

“Rockwool is the right choice for me”

If Rockwool is the brand you need, these are two products we recommend to customers:

• Rockwool RWA45 – Suitable for internal walls, floors and ceilings. This is a dense, multi-purpose slab offering excellent soundproofing and fire resistance properties.
• Rockwool Hardrock – Suitable for a wide range of flat roof applications. This is a dual density, non-combustible insulation board featuring excellent thermal and acoustic properties

“Isover is the right choice for me”

If Isover is the brand you need, these are two products we recommend to customers:

• Isover APR: A denser glass wool solution offering exceptional acoustic performance in partitions, walls and floors.
• Isover Cavity Wall Slabs: A highly dense and durable slab featuring a water repellent binder, ideal for external masonry cavity walls. These are available as 0.032W/mK and 0.036W/mK options.