-
140mm Rockwool Flexi Slab Acoustic Insulation 1200mm x 600mm 2.88m2 Pack
140mm Rockwool Flexi has been designed as a multi-use, dual-purpose acoustic and thermal mineral wool insulation with a unique flexible edge along one side. It is suitable for use all over the home, in pitched roof rafters, framed external walls, internal partitions, intermediate floors, separating walls and floors, and timber suspended ground floors.
£42.01£50.41 Ex VATInc VAT£14.59£17.51 Per m2 Add to cart -
140mm Knauf Rocksilk Flexible Insulation Slab 1200mm x 600mm 2.16m2 Pack
140mm Knauf Insulation Rocksilk Flexible Slab is a Rock Mineral Wool slab, designed for use in multiple thermal and acoustic applications as well as the fire protection of a loft conversion floor. It is non-combustible with the best possible Euroclass A1 reaction to fire classification.
POA Get a quote -
140mm Superglass 32 Timber & Rafter Roll Insulation 3.19m2 Roll
140mm Superglass 32 Timber & Rafter Roll covers 3.19m2, providing snug and energy-saving insulation between timbers and rafters
POA Get a quote -
140mm Superglass Cladding Mat 40 Thermal & Acoustic Roll 8.40m2
140mm Superglass Cladding Mat 40 is a resilient, medium dense and non-combustible glass mineral wool insulation roll with exceptional durability and high tear strength. The roll is supplied 1200mm wide to allow quick installation and minimum on-site cutting and waste.
POA Get a quote -
Buy in Bulk & Save
1-14 15+ £45.77£54.92 £39.82£47.78 
140mm URSA 35 Timber Frame Roll 4.93m2
140mm URSA Timber Frame Roll 35 is a lightweight, non-combustible, glass mineral wool product. It is suitable for use in both timber and metal framed walls.
£45.77£54.92 Ex VATInc VAT£9.28£11.14 Per m2 Get restock alert
140mm Insulation Acoustic Thermal
140mm insulation is a deep insulation thickness used to deliver high thermal performance when strong heat control is needed, rather than a minor thermal improvement. At 140mm, insulation effectively slows heat flow, resulting in more stable indoor temperatures throughout the seasons.
This thickness is typically specified where thermal performance is prioritised over space constraints.
What is 140mm insulation thickness?
140mm insulation thickness describes the depth of the insulation layer after installation – 140 millimetres from the internal (warm) side to the external (cold) side. This depth is often specified because it enables reliable thermal control without stacking multiple layers.
At 140mm thick insulation, heat transfer is slowed enough that indoor temperature changes are more gradual. Warm air stays inside longer during cold weather, and summer heat takes longer to enter the building.
Because 140mm depth takes up more space than lighter options, it is typically incorporated at the design stage.
What is 140mm thick insulation used for?
140mm insulation thickness is usually installed in:
- External walls, including cavity walls and timber or steel frame builds.
- Warm roofs and flat roofs, where depth helps prevent cold spots.
- Floors over unheated spaces, such as garages or voids.
- High-performance refurbishment projects that apply modern standards to older buildings.
Thick 140mm insulation is less common in tight retrofits but commonly specified in new-build construction and extensions designed for energy efficiency.
Types of 140mm insulation
Here’s how the main 140mm insulation options compare:
Glass wool insulation
This is made by spinning molten glass into fibres. At 140mm, it traps a large volume of still air, limiting heat transfer.
- Flexible enough to friction-fit between studs or joists.
- Good at reducing noise as well as heat loss.
- Non-combustible (Euroclass A1 or A2, depending on product)
- Requires careful installation to avoid gaps or excessive compression, which can reduce performance.
Rock Mineral Wool insulation
Produced from volcanic rock, this material is denser than glass wool.
- Strong fire resistance. Typically classified as Euroclass A1 for fire performance
- Holds its shape well at full depth
- Performs reliably in walls, floors, and roofs
- Also helps with sound control
PIR insulation boards
PIR is a rigid foam panel with low heat transfer.
- Delivers high thermal performance for its size
- Keeps its shape and thickness over time
- Foil facings can assist with vapour control and installation detailing
- Requires accurate cutting and tight jointing to maintain performance
Phenolic Foam
This is a high-performance board similar to PIR but with lower thermal conductivity.
- Excellent thermal efficiency.
- More brittle, so careful handling is needed.
- Common in projects with tight energy targets.
Some manufacturers produce wood fibre and specialist foam products at this depth. But these are less common and usually chosen for specific design reasons rather than general trade use.
FAQ
Where to buy 140mm thick insulation?
You can buy 140mm thick insulation online from Insulation Wholesale. We stock multiple materials at this depth, including phenolic foam, PIR, and mineral wool. We supply clear product options, reliable availability, and pricing that works for real projects – whether you are ordering a few boards or a full load. If you need help choosing the right material for your build-up, our team can help.
How to cut 140mm insulation?
- Mineral wool: Use a long insulation knife or saw. Cut a little oversized so it fills the space properly.
- Rigid boards (PIR or phenolic): Score with a sharp blade, then snap over a straight edge.
Always cut on a flat surface for stability. This helps achieve cleaner, more accurate cuts.
How to fix 140mm insulation?
Fixing depends on the product and location:
- Between studs or joists: Friction-fit mineral wool so that it fills the space without sagging.
- Rigid boards on walls or roofs: Fix mechanically using appropriate insulation fixings, then seal all joints.
- Floors: Support insulation fully so it does not drop or bow over time.
- Some systems also require adhesive bonding or taping. Check manufacturer guidance.
Insulation must remain in full contact with the surface it protects. Any air gap becomes a weak point that compromises performance.
