Which insulation to choose for your energy renovation in Luxembourg? Full comparison 2026
Glass wool, stone wool, wood fibre, cellulose wadding, hemp, EPS or polyurethane: each insulation material has its strengths, limitations and direct impact on the Luxembourg Klimabonus. In 2026, material choice goes beyond technical performance — it directly determines your grant amount. A biosourced or mechanically fixed mineral insulation qualifies for 115 euros/m² in Klimabonus, versus only 60 euros/m² for standard materials, and 0 euros for fossil insulators like EPS or PUR. This guide compares all insulation types across 8 criteria to help you make the right choice for your project, your home and your budget.
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Simulate my grantsThe 8 essential criteria for choosing insulation
Choosing insulation is more than comparing figures in a catalogue. In Luxembourg renovation practice, eight criteria determine whether a material suits your project and whether you can extract the maximum grants from it.
Thermal conductivity λ (lambda, W/m·K)
The fundamental measure: the lower λ, the better the insulation at equal thickness. Polyurethane (λ ≈ 0.022–0.028 W/m·K) is the compactness champion; standard glass wool (λ ≈ 0.032–0.044 W/m·K) needs more thickness for the same result. Key formula: R = thickness (m) ÷ λ. It is this R value — not λ alone — that determines the actual performance of your wall.
Thermal phase shift (hours)
Often overlooked, this measures how long summer heat takes to travel through the insulation and warm the interior. A phase shift above 10 hours is recommended for summer comfort without air conditioning. Dense biosourced materials — wood fibre, cellulose wadding, cork — excel here with 10–14 hours. Lightweight glass wool offers only 2–4 hours — insufficient during heat waves. In Luxembourg, where summers are becoming structurally hotter, this criterion is growing in importance.
Moisture management (μ and hygroscopicity)
Biosourced insulators (hemp, wood fibre, cellulose wadding) are hygroscopic — they absorb excess water vapour and release it gradually without loss of performance, naturally regulating the indoor climate. Synthetic insulators (EPS, PUR) block all diffusion and require a carefully, continuously installed vapour barrier. For Luxembourg’s older masonry homes, breathable insulation is often preferable to prevent condensation and mould problems.
Fire reaction (Euroclass)
Mineral wools (glass, stone) are rated A1 or A2: they do not spread fire and release no toxic fumes. Synthetic insulators (EPS, PUR) are combustible (class E to F) and release toxic fumes when burning — hydrogen cyanide in the case of PUR. In attics, technical ducts and at-risk walls, fire reaction can be a binding regulatory constraint.
Environmental impact and embodied energy
Cellulose wadding consumes approximately 30 times less embodied energy to manufacture than polystyrene. Biosourced insulators store carbon and have a very favourable footprint. In Luxembourg, fossil-origin insulators (EPS, PUR, XPS) are excluded from the Klimabonus unless they contain over 50% recycled materials — environmental performance is therefore also a primary economic criterion.
Ease of installation and available forms
Rolls, semi-rigid panels, rigid panels, blown loose-fill, injected fill: the form directly determines possible applications. Blown loose-fill is ideal for irregular lost attics; high-density rigid panels suit EWI; semi-rigid rolls fit into frames for IWI. The available thickness in your home also drives the choice: for a small bedroom IWI, an 8 cm PUR panel may be preferred to 14 cm of glass wool giving the same R — even though the Klimabonus implications differ significantly.
Material + installation cost (euros/m² installed)
Total project cost includes material, installation, finishings (vapour control layer, framing, plasterboard or render) and preparatory work. Glass wool is the cheapest to buy, but IWI installation with metal frame and plasterboard represents the bulk of the total budget. Wood fibre, more expensive to buy, is made competitive by the higher Klimabonus grants and its superior overall performance. For detailed cost comparison, see our guide on insulation costs in Luxembourg.
Klimabonus 2026 eligibility and grant amount
Since 1 January 2026, the Luxembourg Klimabonus distinguishes three insulation categories. Ecological/biosourced materials: 115 euros/m². Mechanically fixed mineral materials: also 115 euros/m². Standard or bonded materials: 60 euros/m². Fossil insulators are no longer subsidised unless over 50% recycled (75 euros/m²). For IWI, a 25% reduction applies to all amounts.
Klimabonus 2026: which insulation maximises your grant in Luxembourg?
The Klimabonus Wunnen scheme, overhauled since 1 January 2026, introduced a fundamental distinction between insulation materials. A key reminder: the Klimabonus agreement in principle must be obtained before starting any work — no exceptions are possible.
| Klimabonus Category | Eligible Materials | Grant — exterior wall (level I) | Key note |
|---|---|---|---|
| Category c — Ecological | Wood fibre, cellulose wadding, hemp, linen, sheep wool, cork, cotton wool, recycled textile | 115 euros/m² | Mechanical fixing required for EWI; not for IWI |
| Category b — Mechanical mineral | Stone wool, glass wool — mechanically fixed | 115 euros/m² | Mechanical fixing required (bonding alone not eligible) |
| Category a — Standard | Bonded mineral wool, EPS with 50%+ recycled content | 60 euros/m² + 15 euros/m² (recycled bonus) | For IWI, all grants reduced by 25% |
| Not subsidised | Standard EPS, PUR, XPS (without 50%+ recycled content) | 0 euro/m² | Excluded (fossil materials) since 2024 |
Source: Guichet.lu — Klimabonus Wunnen, in force since 01/01/2026.
For insulation installed exclusively from the interior (IWI), Klimabonus amounts are reduced by 25%. A biosourced insulation in IWI qualifies for 115 euros × 75% = 86.25 euros/m² instead of 115 euros/m². If you have the choice between IWI and EWI, exterior insulation is doubly advantageous: no loss of living space and grant with no reduction.
Full insulation comparison table 2026
This table covers the 8 most commonly used insulation materials in Luxembourg residential renovation. λ values are typical declared values — always check the technical documentation of your chosen product. Prices are indicative ranges for the complete project (material + installation + finishings) for a standard Luxembourg residential job in 2026, 3% VAT included.
| Insulation | λ (W/m·K) | Phase shift | Fire reaction | Moisture | Thickness R=4 | Klimabonus 2026 | IWI installed (euros/m²) |
|---|---|---|---|---|---|---|---|
| Glass wool | 0.032–0.044 | 2–5 hrs ⚠ | A1–A2 ✓✓ | Hydrophobic | 13–17 cm | 60–115* | 70–95 |
| Stone wool | 0.034–0.045 | 3–6 hrs ⚠ | A1–A2 ✓✓ | Hydrophobic | 14–18 cm | 60–115* | 75–100 |
| Wood fibre | 0.036–0.050 | 10–14 hrs ✓✓ | D–E | Hygroscopic ✓✓ | 15–20 cm | 115 | 90–130 |
| Cellulose wadding | 0.038–0.042 | 8–12 hrs ✓ | D–E | Hygroscopic ✓✓ | 15–17 cm | 115 | 75–110 |
| Hemp | 0.039–0.045 | 8–12 hrs ✓ | D–E | Hygroscopic ✓✓ | 16–18 cm | 115 | 80–120 |
| EPS (polystyrene) | 0.030–0.038 | 2–4 hrs ⚠ | E–F ⚠ | Airtight | 12–15 cm | Not sub. / 75* | 55–80 (EWI) |
| Polyurethane (PUR) | 0.022–0.028 | 1–3 hrs ⚠ | E–F ⚠ | Airtight | 9–11 cm | Not subsidised | 70–95 |
| Expanded cork | 0.036–0.042 | 10–14 hrs ✓✓ | D–E | Moisture resistant ✓✓ | 15–17 cm | 115 | 100–145 |
* Mineral wool: 115 euros/m² if mechanically fixed; 60 euros/m² if bonded. EPS: 0 euro/m² if standard; 75 euros/m² (60+15) if 50%+ recycled content. For IWI, apply a 25% reduction to all amounts. Sources: Guichet.lu Klimabonus Wunnen — in force since 01/01/2026; price data from Renov.lu certified partner craftspeople — Luxembourg 2026.
Glass wool — the versatile budget option
Glass wool is Europe’s most widely used insulation. Made from recycled glass (60–80% of its composition), it comes as rolls, semi-rigid panels or blown loose-fill. Its thermal conductivity ranges from λ = 0.032 to 0.044 W/m·K depending on density. It is available at all Luxembourg builders’ merchants and mastered by almost all insulation contractors.
Strengths: lowest purchase price, good fire resistance (class A1 or A2), wide range of products and thicknesses, easy installation. Weaknesses: low thermal phase shift (2–5 hours), vapour control layer required in IWI, irritating without PPE. Not suitable for damp zones without additional protection.
In IWI with mechanical fixing in a frame (standard technique): 115 euros/m² x 75% = 86.25 euros/m². In EWI with mechanical fixing (ventilated cladding): 115 euros/m². If simply bonded in EWI: 60 euros/m². Check with your installer which fixing method will be used before submitting your Klimabonus application.
Stone wool — the fire-resistant choice
Made from volcanic rock (primarily basalt) melted at very high temperatures (around 1,500°C), stone wool outperforms glass wool in two key areas: mechanical resistance and fire behaviour. Its higher density — up to 160–200 kg/m³ for rigid EWI panels — provides better long-term stability and useful rigidity for cladding systems. Typical thermal conductivity is λ = 0.034 to 0.045 W/m·K.
Its thermal phase shift (3–7 hours depending on density) remains lower than biosourced materials. Dense stone wool (80+ kg/m³) offers a noticeably better phase shift than lightweight grades. It is widely used in ventilated cladding EWI systems and in areas requiring specific fire resistance.
Same rules as glass wool: 115 euros/m² in EWI or IWI with mechanical fixing (category b); 60 euros/m² if bonded (category a). For IWI, apply the 25% reduction. Stone wool is particularly well-suited for ventilated cladding EWI, which maximises the Klimabonus (115 euros/m² with no reduction).
Wood fibre — summer comfort champion
Wood fibre is produced by defibering wood offcuts or otherwise unusable timber — often sawmill residues. It is the biosourced insulation offering the best balance between winter thermal performance, exceptional summer comfort and hygric qualities. Thermal conductivity ranges from λ = 0.036 to 0.050 W/m·K depending on density.
Its key differentiator is thermal phase shift: 20 cm of dense wood fibre panel can achieve 12–14 hours. If the south façade peaks in heat at 2pm, your interior won’t feel that heat until the middle of the night — by which time nocturnal ventilation will have already naturally cooled the interior air. Wood fibre is also hygroscopic, naturally regulating indoor humidity and adapting perfectly to traditional Luxembourg masonry homes.
Category c (ecological): 115 euros/m² in EWI, 86.25 euros/m² in IWI (after 25% reduction). Combined with the Klimaprêt (up to 100,000 euros) and Enoprimes, wood fibre becomes very cost-competitive despite its higher purchase price.
Cellulose wadding — the accessible biosourced option
Cellulose wadding is made from recycled newspaper and paper (80–85% of its composition), treated with fire retardant and pest-resistant agents. Thermal conductivity is λ = 0.038 to 0.042 W/m·K. It stands out on three complementary criteria: thermal phase shift (8–12 hours), moisture regulation and an exceptional environmental footprint — it consumes approximately 30 times less embodied energy than polystyrene.
Available as blown loose-fill for lost attics (preferred use), semi-rigid panels for IWI in frames, or injected into timber-frame walls. Blown installation in lost attics is particularly fast — often one day for an entire home — and leaves no uncovered areas.
Blown loose cellulose wadding is sensitive to progressive settling over time, particularly on vertical walls. Ensure your installer uses sufficient density (minimum 45–55 kg/m³ injected in walls, 25–30 kg/m³ blown on horizontal lost attics).
Category c (ecological): 115 euros/m² in EWI, 86.25 euros/m² in IWI. It likely offers the best performance/price/Klimabonus ratio among all biosourced insulators, particularly for lost attics and timber-frame construction.
Hemp — the natural moisture regulator
Industrial hemp is grown without pesticides or herbicides, and processed into rolls or semi-rigid panels. Thermal conductivity is λ = 0.039 to 0.045 W/m·K. Its most remarkable characteristic is moisture management: hemp can absorb up to 30% of its weight in water vapour and release it gradually without loss of thermal performance. This makes it the insulation of choice for old stone, rubble or brick homes — typical of Luxembourg’s pre-1950 built heritage. Hemp is often used without a vapour barrier thanks to its natural moisture management capacity.
Category c (ecological): 115 euros/m² in EWI, 86.25 euros/m² in IWI. Ideal for Luxembourg’s stone or brick homes where moisture management is a key durability concern. For interior wall insulation (IWI) in old Luxembourg masonry, hemp is often the most technically secure solution.
EPS (expanded polystyrene) — budget EWI solution, but excluded from standard Klimabonus
Expanded polystyrene (EPS, also sold as Styropor®) has historically been the dominant insulation for exterior wall insulation in Europe. Thermal conductivity is λ = 0.030 to 0.038 W/m·K (grey graphite EPS reaches λ ≈ 0.031 W/m·K). Its low cost and mature application systems make it still the reference for EWI with thin render in France and Belgium.
Strengths: low surface cost, good moisture resistance, wide network of qualified contractors, easy to cut. Major limitations: very low thermal phase shift (2–4 hours), combustible (class E to F) with toxic fumes in fires, high carbon footprint, and — crucially — excluded from the 2026 Klimabonus in its standard form since 2024. Only EPS containing at least 50% recycled materials qualifies for a reduced grant (75 euros/m² in EWI).
Standard EPS (without 50%+ recycled content) is completely excluded from Klimabonus since 2024. If your installer proposes EPS, demand the product’s FDES (environmental declaration sheet) to confirm the recycled content. Without this documented confirmation before work starts, your Klimabonus application will be rejected.
Polyurethane (PUR) — high performance in thin profile
Polyurethane (PUR) is the best-performing synthetic insulation on the mass market: thermal conductivity reaches λ = 0.022 to 0.028 W/m·K for rigid foams. To achieve R = 4, only 9–11 cm is needed versus 13–18 cm for mineral wools — decisive for IWI in small rooms. PUR comes as rigid foam panels or in-situ sprayed foam. Key limitations: fossil material, fire reaction class E or F with extremely toxic gas release (hydrogen cyanide), minimal thermal phase shift (1–3 hours), very low vapour permeability. Critically: PUR is completely excluded from Luxembourg’s Klimabonus since 2024, with no exceptions.
When to use it despite Klimabonus exclusion? PUR remains relevant where space is truly critical: under-screed floor insulation (basement, ground floor) where compression resistance is key. For basement and floor insulation, see our dedicated guide.
Expanded cork — the premium solution
Expanded cork is made from the bark of the cork oak (Quercus suber), harvested without felling the tree — the cork oak can be stripped every 9–12 years for 150–200 years. It stands apart through one unique characteristic: natural moisture resistance without any chemical treatment. Cork is rot-proof, impervious to mould, rodents and insects, and maintains its performance in humid environments or direct ground contact. Thermal conductivity is λ = 0.036 to 0.042 W/m·K.
Its exceptional thermal phase shift (10–14 hours) matches dense wood fibre. It also offers excellent acoustic performance — dual thermal and acoustic function — particularly valued for floors, foundations and party walls. Its main limitation is its higher cost (100–145 euros/m² installed IWI).
Category c (ecological): 115 euros/m² in EWI, 86.25 euros/m² in IWI. Particularly suited for foundations, buried walls and damp rooms where other biosourced materials would degrade. For basement floor and slab insulation, high-density cork (120+ kg/m³) is the only biosourced Klimabonus-eligible alternative to PUR.
Which insulation for your Luxembourg home?
Every home is unique. Our experts analyse your situation — wall type, moisture, available space, budget, target CPE class — and guide you to the best insulation with a transparent quote integrating your Klimabonus grants.
Which insulation for which zone? Practical guide for Luxembourg
The right insulation depends as much on the area to be treated as on the material itself. Here are recommendations adapted to the specific Luxembourg context: predominantly older housing stock (60–70% of homes built before 1980), temperate continental climate, and 2026 Klimabonus rules. For an overview of energy class improvement strategies, see our dedicated guide.
Exterior walls — EWI
First choice: high-density rigid wood fibre panels (exceptional phase shift, 115 euros/m² Klimabonus). Second choice: stone wool in ventilated cladding (115 euros/m² if mechanically fixed). EPS only viable with 50%+ recycled content; in standard form, no Klimabonus grant. Avoid PUR in EWI.
Walls — IWI
For old stone or brick homes — typical of historic districts in Luxembourg City, Esch-sur-Alzette, Dudelange — always prefer breathable hygroscopic insulators: hemp or wood fibre. For newer concrete or aerated concrete homes, stone wool or glass wool in metal frame is economical and effective. See our guide on interior wall insulation (IWI).
Lost attics
Blown cellulose wadding is the optimal choice: excellent biosourced value for money, 8–12 hour phase shift, outstanding carbon footprint, Klimabonus eligible. See our guide on roof and attic insulation in Luxembourg.
| Zone | 1st choice (performance + Klimabonus) | 2nd choice (value for money) | Avoid (excluded from Klimabonus) |
|---|---|---|---|
| Walls — EWI | HD Wood fibre (115 euros/m²) | Stone wool cladding (115 euros/m²) | Standard EPS, PUR |
| Old walls — IWI | Hemp (86.25 euros/m²) or wood fibre | Mech. fixed stone wool (86.25 euros/m²) | PUR (0 euro/m²) |
| Lost attics | Blown cellulose wadding (115 euros/m²) | Glass wool rolls (86.25 euros/m²) | EPS, PUR |
| Ground floors | HD cork (115 euros/m² — Klimabonus) | HD EPS/XPS (no Klimabonus) | Mineral wools (poor compression) |
| Pitched roof | Semi-rigid wood fibre (86.25 euros/m²) | Blown cellulose wadding | EPS, PUR |
Frequently asked questions about insulation in Luxembourg
Is polystyrene (EPS) still subsidised in Luxembourg?
No, in its standard form, EPS has not been eligible for Klimabonus since 2024. Only EPS containing at least 50% recycled materials qualifies for a reduced grant of 60 + 15 = 75 euros/m² in EWI (before the 25% IWI reduction). Always demand the product’s FDES to confirm the recycled content before submitting any Klimabonus application.
What is the difference between λ (lambda) and R when choosing insulation?
Lambda (λ) is an intrinsic material property: thermal conductivity in W/m·K. The lower λ, the better the insulation at equal thickness. R (thermal resistance) takes into account the installed thickness: R = thickness (m) ÷ λ. R determines your insulation’s actual real-world performance. The Klimabonus imposes minimum R values — for exterior walls generally R ≥ 3.5 m²·K/W for grant level I and R ≥ 5 m²·K/W for level II.
Do biosourced insulators really outperform mineral wools?
In terms of pure thermal conductivity (λ), no: mineral wools are comparable or slightly better at equivalent thickness. But biosourced materials clearly outperform mineral ones on two criteria that matter for real comfort: thermal phase shift (summer comfort, crucial in non-air-conditioned homes) and moisture regulation (winter comfort in old homes). The Klimabonus rewards them at the same rate as mechanically fixed mineral insulation (115 euros/m²).
Does the 3% VAT rate apply to insulation work in Luxembourg?
Yes. Energy renovation work on residential properties more than 2 years old in Luxembourg benefits from a reduced VAT rate of 3% (instead of 17%). This applies to insulation work (supply + installation + finishings) and related advisory services. This reduction is fully stackable with Klimabonus and Enoprimes grants.
Take action — compare quotes and maximise your grants
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