Knauf vs Isover | Which is better?

Is Isover and Knauf fire-resistant?

Both brands achieve a Euroclass A1 fire rating, which means they do not contribute towards the spread of fire or toxic smoke.

However, they are not 100% fireproof and will melt under extreme temperatures. If you’re insulating in applications where fire safety protocols are in the highest demand, such as partition walls and ceilings, you should use insulation made from rock mineral wool, such as Knauf’s RockSilk, or Rockwool.

These are made from volcanic rock, which does not melt and can withstand extremely high temperatures over 1,000°C.

What is thermal drift?

Another factor to consider with insulation is thermal drift.

Over time, insulation naturally weakens. This could be due to material composition, exposure to moisture, or the building settling. This gradual decline is known as thermal drift, and it results in the R-value reducing (the measure of thermal resistance).

Fibreglass insulation is light, fluffy, and doesn’t hold its shape particularly well. Over time, it can sag or compress, leading to gaps which allow heat to escape. Its thermal performance also drops significantly if it becomes damp, as moisture displaces the air pockets that are crucial to insulation.

Using two insulators alongside each other

Fibreglass insulation has many benefits, with fire resistance and sound absorption being two of the biggest ones. These are two benefits that you don’t get from PIR insulation, which is purely designed for thermal performance. 

As PIR insulation is incredibly thin, it can be used in conjunction with fibreglass insulation to get the best of both worlds, allowing you to achieve target U-values for energy efficiency while also enhancing fire safety, sound absorption and durability.

Which is cheaper?

Cost is often the biggest deciding factor when it comes to insulation, with how much you spend being a big difference maker in finishing your project on time or being delayed.

It’s important to consider the upfront costs, long-term costs and potential energy savings you can make down the line.

Upfront costs – Price per Square Meter

• Knauf typically ranges between £2–£9/m²
• Isover typically ranges between £2–£10/m²

Long-term costs – Energy Efficiency & Savings

Regardless of the brand you go with, the choice to insulate your home will save you on energy costs, with the average home reducing energy costs by 50% a year (anywhere from £300 to £500).

Both Knauf and Isover offer very similar insulation, with comparative batt and roll products for most applications sharing the same thermal conductivity rating. For most applications, Knauf will be the more budget-friendly solution.