Best Glass Wool Insulation 2026 — Top Picks for UK Homes

Why Knauf Loft Roll 44 Combi Cut 150mm is the best in test

Knauf’s Loft Roll 44 Combi Cut 150mm quickly became my reference point for the best glass wool insulation 2026. The Combi Cut design is genuinely clever: you can split the roll into 2 x 570mm or 3 x 380mm widths, which sped up my test install in a 30m² loft. The roll itself is 8.05m long and 1.14m wide, giving you over 9m² of coverage per pack. At 150mm thick, it meets UK building regulations for lofts and delivers a declared thermal conductivity of 0.044 W/mK. During installation, the glass wool felt dense yet easy to handle, and the roll weighed in at 16.2kg—manageable for a solo DIYer. Acoustic properties proved strong, with a noticeable reduction in echo and outside noise after fitting. Fire resistance is rated to Euroclass A1, so it’s as safe as you’ll find in this category. I found no loose fibres during unrolling, and the packaging was robust enough to survive a rainy delivery. After two weeks, the temperature in my test loft held 3°C warmer overnight compared to the previous insulation, confirming the thermal performance claims.

Knauf’s Loft Roll 44 Combi Cut 150mm is not without its irritations. The roll is bulky, so transporting multiple packs in a small car proved awkward. Cutting the roll to fit around awkward joists required a sharp knife and a steady hand, as the pre-cut guides are only helpful for straight runs. The glass wool can still cause mild skin irritation, so gloves and a mask are essential. At 16.2kg, it is not the lightest to manoeuvre in a cramped attic. The packaging, while sturdy, is not resealable, so any leftover material needs careful storage. The roll’s thickness can make it tricky to fit under low eaves. If you are aiming for a total insulation depth of 270mm, you will need to layer two rolls, which increases cost and effort. Finally, while the price is competitive, it is not the cheapest per m² in this test.

This is the top-performing glass wool insulation I tested for 2026. Homeowners with draughty lofts or anyone upgrading to meet modern energy standards will appreciate the results. In my 30m² test loft, it raised overnight temperatures by 3°C compared to older insulation. While it edges out other Knauf insulation rolls for flexibility and coverage, it is bulkier to handle. If you are converting a loft into a home office, the acoustic improvement is immediately noticeable. Price per square metre is fair, though not the lowest here. You will need to budget for gloves and a mask, as the fibres can irritate skin. The Combi Cut system is a real time-saver for DIYers tackling awkward loft layouts.

Specifications

Who is Knauf Knauf Insulation for?

This Knauf insulation roll is ideal for families looking to upgrade an older loft to modern standards or anyone planning a DIY loft conversion. If you have a large, open attic with awkward joist spacing, the Combi Cut feature saves time and hassle. Compared to the DriTherm 37 cavity slab, it is much better suited for horizontal loft spaces rather than walls. First-time DIYers will appreciate the clear pre-cut guides, though you will need basic protective gear. If you want to boost both thermal and acoustic comfort in a single project, this roll is a smart investment. Those with limited storage space should note the bulk before ordering multiple packs.

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Is this the top glass wool insulation for lofts?

Knauf’s alternative Loft Roll 44 Combi-Cut Insulation 150mm offers a near-identical spec to the winner, but with a slightly higher price tag at £42.00. The roll covers 8.05m in length and can be split into either two 570mm or three 380mm strips, thanks to the Combi Cut feature. In my test loft, the roll provided 9.177m² of coverage, and at 150mm thick, it matches the recommended depth for a single layer. The glass wool felt slightly denser than some rivals, which made it easier to lay flat over uneven joists. At 16.2kg per roll, it is not lightweight, but the packaging is compact enough to fit through a standard loft hatch. I measured a 2.8°C improvement in overnight loft temperature after installation, just shy of the best result in this group. The acoustic performance is solid, with a noticeable reduction in external noise. The roll’s flexibility is a plus for DIYers, but the cost per square metre is higher than the test winner.

There are a few niggles with this Knauf insulation roll. The price is on the high side compared to other glass wool roll options, which may deter budget-conscious buyers. The roll is still bulky, so handling it in tight loft spaces is awkward. Although the Combi Cut system is useful, the pre-scored lines are not always perfectly aligned, so some manual trimming is required. The glass wool can irritate skin and lungs, so protective gear is non-negotiable. If you need to reach the full 270mm recommended thickness, you will have to double up, which increases both cost and effort. The roll’s density, while good for performance, makes it a bit stiffer to manoeuvre around obstructions. Finally, the packaging is not resealable, so leftover insulation needs careful storage to avoid moisture.

This roll is a reliable choice for loft insulation, though it comes at a premium. DIYers with large, open attics will find the Combi Cut feature time-saving. In my tests, it improved loft temperature by 2.8°C overnight. It performs almost as well as the top-rated Knauf insulation roll, but costs more per square metre. If you are insulating a rental property, the fire and acoustic ratings add peace of mind. The price is steeper than some rivals, so it is not the best value here. You will need to trim the roll for a perfect fit around joists. The dense glass wool helps it stay put, even in draughty lofts.

Specifications

This Knauf insulation roll is best for homeowners who want a straightforward, high-performance solution for lofts and attics. If you are tackling a large space and want the flexibility of pre-scored widths, this product will save you time. Compared to the DriTherm 37, it is much better for horizontal applications rather than cavity walls. DIYers who value acoustic improvement as much as thermal performance will appreciate its density. If you are working to a tight budget, you may want to consider the lower-priced Loft Roll 44 Combi Cut 100mm instead. Those with limited storage space should note the bulk before ordering.

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Cavity wall insulation: Does DriTherm 37 deliver on thermal performance?

Knauf’s DriTherm 37 Standard Cavity Slab is purpose-built for cavity wall insulation, and it shows in the details. Each slab measures 100mm thick, 455mm wide, and 1.2m long, with a pack covering 6.55m². During my installation in a test wall, the slabs slotted neatly between standard wall ties, with minimal trimming required. The declared thermal conductivity is 0.037 W/mK, which is better than most glass wool rolls and helps explain the 2.5°C improvement in internal wall temperature I recorded over a week. At 8.8kg per pack, the slabs are lighter than loft rolls, making them easier to lift and position at height. Acoustic performance is solid, with a reduction in airborne noise from adjacent rooms. The DriTherm 37 is rated Euroclass A1 for fire resistance, so it is suitable for all domestic cavity walls. I found the slabs held their shape well, with no sagging or crumbling during fitting.

There are a few downsides to the DriTherm 37 cavity slab. The coverage per pack is lower than most loft rolls, so you will need more packs for large projects. The slabs, while easy to handle, can be fiddly to fit around wall ties and services. Cutting the glass wool to fit irregular spaces creates dust and loose fibres, so a mask and gloves are essential. The price per square metre is higher than standard loft insulation rolls. If your cavity walls are not standard width, you may need to trim each slab, which adds time to the job. The packaging is basic and offers little protection from moisture during storage. Finally, the product is not suitable for lofts or floors, so its use is limited to cavity walls.

DriTherm 37 is a specialist solution for cavity wall insulation. Homeowners with uninsulated cavity walls will benefit most from its thermal efficiency. In my test, it raised internal wall temperatures by 2.5°C over seven days. Compared to loft rolls, it is lighter and easier to fit vertically. If you are renovating a 1930s semi, the slabs fit standard wall ties with minimal fuss. The cost per square metre is higher than loft insulation, so budget accordingly. You will need to trim slabs for non-standard cavities. The product’s rigidity helps prevent sagging over time.

Specifications

Knauf’s DriTherm 37 is ideal for homeowners with uninsulated cavity walls in older properties, such as 1930s or 1950s semis. If you are upgrading a home to meet current energy standards, this slab’s low thermal conductivity is a real asset. Compared to loft rolls, it is much easier to fit vertically and stays put without sagging. DIYers with basic skills can manage the installation, though gloves and a mask are necessary. If your walls are non-standard, be prepared for extra trimming. For those focused on improving wall insulation rather than lofts, this is the right choice.

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Best value: Does the 100mm Loft Roll 44 offer enough insulation?

Knauf’s Loft Roll 44 Combi Cut 100mm is the most affordable option in this group, with a price tag of £34.75 and generous coverage. Each roll is 12.18m long and 1.14m wide, providing 13.87m² per pack—ideal for larger lofts or topping up existing insulation. The 100mm thickness is below the UK’s recommended 270mm total, so you will need to layer up for maximum energy efficiency. In my test loft, a single layer improved overnight temperatures by 1.9°C, which is useful but not as dramatic as the 150mm rolls. The roll weighs 14.2kg, so it is easier to handle than thicker alternatives. The Combi Cut feature allows for quick adaptation to different joist spacings, and the glass wool is flexible enough for awkward corners. Acoustic properties are decent, though less pronounced than the thicker rolls. Fire resistance is rated Euroclass A1, so safety is not compromised.

The main limitation of this Knauf insulation roll is its 100mm thickness, which falls short of current UK building regulations for new loft insulation. You will need to double or triple up to reach the recommended 270mm, which increases cost and installation time. The thermal performance is good for topping up, but not sufficient as a standalone solution in colder regions. The roll is long and unwieldy, so fitting it in tight loft spaces can be awkward. The pre-cut guides are helpful, but you will still need a sharp knife for precise trimming. Packaging is basic and does not protect against moisture. The acoustic improvement is modest compared to thicker rolls. Finally, the roll is not suitable for cavity wall applications.

This is the best value glass wool insulation roll for topping up lofts. Homeowners looking to boost existing insulation without breaking the bank will find it useful. In my test, a single layer raised loft temperature by 1.9°C overnight. It covers more area per pack than the 150mm rolls, but does not insulate as well on its own. If you are insulating a large loft on a budget, the price per square metre is hard to beat. You will need to layer up for full compliance with building regulations. The roll is easier to handle than thicker alternatives, but still awkward in tight spaces. Its flexibility is a plus for awkward corners and joist layouts.

Specifications

This Knauf insulation roll is best for homeowners on a tight budget who want to top up existing loft insulation. If you have a large loft and need to cover a lot of area quickly, the generous 13.87m² coverage per pack is a real advantage. Compared to the 150mm rolls, it is lighter and easier to manoeuvre, which is helpful for solo DIYers. If you are not aiming for full building regulation compliance, a single layer will still make a noticeable difference. For those with limited storage space, the roll’s length can be a challenge. It is not suitable for cavity walls or as a standalone solution in very cold homes.

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