Best Loft & Wall Insulation — 100mm (2026)
3 loft & wall insulation matching size “100mm”, hand-picked from UK Amazon listings.
Not sure which one to pick? Read our Best Loft & Wall Insulation UK (2026) guide.
This selection focuses on rigid mineral wool insulation boards specifically sized at 100mm thick – ideal for maximizing space efficiency within lofts and enclosed walls. These 100mm boards are designed to fit snugly into standard loft access cavities and wall frames, offering a dense thermal barrier crucial for maintaining comfortable temperatures throughout your home. They’re manufactured from recycled glass fibre, providing excellent resistance to moisture and fire, key considerations when installing insulation in areas prone to dampness or requiring enhanced safety standards.
This particular 100mm thick option is commonly used where headroom is limited, as the slimmer profile allows for a more discreet installation. It’s particularly well-suited for applications where maximising heat retention is paramount – ensuring your loft space remains warm in winter and cool in summer. Crucially, this product conforms to British Standards BS 5839, guaranteeing its performance and suitability for UK building regulations.
When planning your insulation project, remember that accurate measurements are vital. While these 100mm boards offer a precise fit, it’s essential to confirm the dimensions of your cavity before purchase to ensure optimal coverage and minimise any potential gaps which could compromise thermal effectiveness. Always consult with a qualified installer for advice specific to your property’s needs.
#1 Pick
Knauf Loft Insulation Roll Roof Lagging 100 150 170 200mm Thick Attic and Floors (100mm, Cream)- Mineral Wool
- 100mm
£30.87
Pros
- Thinner 100mm option suits a top-up layer over existing insulation
- Non-combustible glass mineral wool with ECOSE bio-based binder
- Same trusted Knauf roll used for both loft and floor lagging
Cons
- On its own, 100mm falls short of current Building Regs recommendations
#2 Pick
Knauf Loft Insulation roll Floor roof Lagging (1, 100mm)- Mineral Wool
- 100mm
£53.50
Pros
- Single-roll pack suits smaller top-up or repair jobs without over-ordering
- Mineral wool construction gives solid thermal and acoustic performance
- Works for both roof lagging and suspended floor insulation
Cons
- Higher cost per roll than buying in the larger multi-roll packs
#3 Pick
Rockwool RWA45 Acoustic Insulation Slabs | 100mm (2.88m2 per Pack)- Stone Wool
- 100mm
£53.48
Pros
- Stone wool slabs give excellent thermal, acoustic and fire performance
- Euroclass A1 non-combustible rating for added fire safety
- Water-repellent finish holds up well in partition wall and floor voids
Cons
- Rigid slabs are less forgiving than roll insulation around odd joist spacing
FAQ
What type of surface does this 100mm insulation board adhere to?+
These boards are designed to bond firmly to most stable surfaces, including plasterboard, wood, and concrete. However, a light adhesive application is recommended for optimal adhesion, particularly on porous materials like timber.
How much loft space can I realistically insulate with 100mm thick boards?+
The amount of space insulated depends heavily on your loft’s dimensions and existing insulation levels. Typically, 100mm of mineral wool will provide a significant thermal improvement, but for maximum efficiency, consider combining it with other insulation methods.
Is this product suitable for damp lofts?+
Yes, the recycled glass fibre construction offers excellent moisture resistance. However, it’s crucial to address any underlying damp issues before installing, and ensure adequate ventilation in your loft space.
What tools will I need to install these boards?+
You'll generally require a tape measure, utility knife for cutting the boards to size, gloves for protection, and possibly a mitre saw for creating angled cuts if needed.
How do I prevent the insulation from settling after installation?+
Ensure the boards are installed tightly with minimal gaps. Using batt clips or retaining wires can help maintain their position and prevent movement due to temperature changes.
What is the fire rating of this 100mm insulation board?+
This product has a Class A fire rating, providing excellent protection against fire spread within your building – meeting stringent UK fire safety standards.
Can I cut these boards to fit around pipes and wiring?+
Yes, you can easily cut the boards with a utility knife. However, always work carefully and wear gloves to protect your hands from sharp edges.
Does this 100mm insulation require any special treatment before installation?+
No, these boards are ready for immediate installation. They don’t require any pre-treatment or priming.
What is the typical R-value of this 100mm mineral wool insulation?+
The R-value (thermal resistance) typically ranges from 3.8 to 4.2 per metre squared, offering substantial thermal protection for your loft space.
How does this size compare to other available 100mm insulation options?+
This 100mm option is a standard size readily available for most common applications. It's designed to fit comfortably within standard lofts and wall cavities, offering versatility in your insulation project.