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Rockwool Flexi Slab (3 Products)

Kill sound in its tracks with Rockwool Flexi acoustic insulation slabs: a multi-use, thermal, acoustic and fire insulation solution with a unique flexible edge along one side. These vibration-trapping beauties reduce sound transmission from inside and outside your home, making your abode a place of zen. 
We stock Rockwool Flexi insulation slabs that are ideal for internal walls, internal floors, and external walls. 

Find Out More About Our Types of Rockwool Flexi Slab
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Rockwool Flexi Slab

What Is Rockwool Flexi Insulation?

Rockwool Flexi insulation slab is a thermal mineral wool insulation, perfect for people who want to insulate their homes against unwanted noise. By introducing Rockwool Flexi acoustic isolation into your home, you will also realise a thermal benefit which can positively impact heating bills by minimising the overall use of energy in your home.

The slabs are composed of rock mineral wool, a material well-known for its great fire-resistant properties and its ability to reduce heat loss. The raw materials used in the manufacturing process are renewable, making Rockwool slabs the go-to choice for the sustainably savvy amongst you.

Thanks to this same manufacturing process, the slabs are extremely dense. The thousands of fine fibres inside each rock mineral wool slab trap thousands of pockets of still air. These air pockets essentially dissipate and dampen sound vibrations when they travel through the insulation fibres; this density plays a vital role in reducing and eliminating unwanted sound from your space.

These 1200mm x 600mm slabs are available in 50mm, 100mm, and 140mm thicknesses. 

Patented Flexible Edge

Rockwool Flexi is an acoustic, fire and thermal insulation solution that reduces sound transmission between spaces. As the name suggests, Rockwool Flexi slabs have a flexible edge along one side. This edge makes them much easier to install than other rock mineral wool slabs. It creates a bridge between the insulation and the supporting framework. The perfect friction fit means that you do not need to cut your slabs and waste materials. 

We recommend Flexi products for people who want to friction fit insulation between framed external walls, rafters, floors, and partitions. You can fit Rockwool Flexi insulation slabs between fresh timber to overcome issues with fresh timber shrinkage; as the timber dries out and shrinks, the rock mineral wool insulation will expand to meet the surrounding framework. 

You can also install Rockwool Flexi insulation slabs in internal and suspended structures. Whether you want to reduce sound transmission between floors or walls, you can expect superior protection with these slabs. 

Frequently Asked Rockwool Flexi Slab Questions

Frequently Asked Rockwool Flexi Slab Questions 

Benefits of Rockwool Flexi Insulation Slabs?


Rockwool has over 80 years of experience manufacturing stone wool products, making them trusted experts in their field; they have been perfecting sound-deadening insulation since the 1900s. There are lots of benefits to choosing these slabs for your home:

  • Fire rating – These slabs have an A1 rating on the Euroclass scale, which means that they are non-combustible.
  • Water-resistance – These slabs are resistant to moisture. The materials inside the slabs do not encourage the growth of rot or bacteria. 
  • Eco-friendly – Flexi slab insulation is made from renewable materials, meaning they will reduce the overall carbon footprint of your home. They are created from between 16% and 40% recycled materials. 
  • Density – The materials and manufacturing process means that these slabs are extremely dense. Dense materials are perfect for people who want to reduce sound transmission. 
  • Thermal conductivity -  50mm and 100mm thick Flexi slabs have a thermal conductivity rating of 0.038 W/mK. The 140mm thick slab has a thermal conductivity rating of 0.035 W/mK. This means that, in addition to their sound absorption properties, they also retain heat well.
  • Flexible edge – These are the only slabs in the Rockwool range that have a flexible edge, which helps when friction fitting between studwork.


Are Rockwool Flexi Slabs Fireproof?

Rockwool Flexi slabs are classed A1 on the Euroclass scale, which means they achieve the highest rating for non-combustibility and fire performance, and are completely non-flammable. 

If you were to hold a blowtorch next to a piece of Rockwool insulation, it might begin to glow but it will not catch fire or melt, making it an excellent fire barrier solution.

Are Rockwool Flexi Slabs Waterproof? 

Flexi slabs are waterproof, making them perfect for homeowners who live in high rainfall areas. If a large amount of water comes into contact with the slabs, the exterior will repel it and the water will simply drain away. Even if the slabs become wet, they can be dried and still retain the same thermal and acoustic properties. However, whilst they are water-resistant, they are not resistant to water vapours in the air. 

Are Rockwool Flexi Slabs Resistant to Mould?

Flexi slab insulation does not promote the growth of mould. There are no organic materials inside the slabs, which means that there is no source of food for mould to grow on. Mould can have a negative impact on the structural integrity of your insulation and pose a threat to the long-term benefits associated with insulating your property. 

Rockwool Flexi insulation has been tested against ASTM C1338. This is one of the standard tests that regulators use to assess whether or not an insulation material will grow mould. Rockwool Flexi slabs have been proven to have zero fungal growth.  

Where Can I Use Rockwool Flexi Slabs? 

The slabs can be used all over the home: in pitched roof rafters, framed external walls, internal partitions, intermediate floors, separating walls and floors, and timber suspended ground floors.
The slabs can be used for the following:

  • Interior timber or steel partition walls
  • Interior timber frame floors
  • Interior timber frame ceilings
  • Acoustic ceilings and partition panels
  • I-joist interior partitions
  • Party walls


How to Cut Rockwool Flexi Slabs?

Like the other slabs in the Rockwool range, Rockwool Flexi slabs are extremely easy to cut. We recommend marking the measurements you need on the slab before cutting so everything's nice and mapped out - preparation is key.  We recommend using a serrated knife to cut Rockwool slabs.

As always, we encourage our customers to take proper safety precautions during any general building projects. You should always use safety goggles and even gloves when cutting materials. We also advise cutting the slabs in a large, clear space with appropriate ventilation. If you have any safety concerns, contact a professional.