5 natural-fibre insulation systems compared – which one suits you?
From hemp-lime and wood fibre to lime insulating plaster: find the right system for your project – with all λ-values, areas of application and strengths at a glance.
Go directly to: IsoHemp hemp blocks · Gutex wood fibre · Hessler insulating plaster · Conluto light clay · Gutex Thermoflex · FAQ
Quick comparison: all 5 systems at a glance
The key figures – scroll down to each system for the detailed advantages and disadvantages.
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Insulation system
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λ value
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Main application
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Application method
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Life cycle assessment
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| IsoHemp hemp blocks | ≈ 0,071 W/mK | External wall, new build, renovation | Masonry | Speichert CO₂ |
| Gutex wood fibre | 0,040 W/mK | Internal/external insulation, rafters | Boards | Renewable |
| Hessler insulating lime plaster | 0,08 W/mK | Internal insulation, listed buildings | Plaster direct | Mineral |
| Conluto light clay | 0,21 W/mK | Infills, cavities, walls | Pouring | Regional |
| Gutex Thermoflex | 0,036 W/mK | Drywall construction, between-rafter insulation | Clamping | Renewable |
System 1 of 5 · λ ≈ 0,071 W/mK
IsoHemp hemp blocks
Insulating and building in one
IsoHemp hemp blocks made from hemp shiv and lime act as both a load-bearing element and thermal insulation, with no need for a separate insulation layer. Ideal for new builds and complete refurbishments where the external wall is to be built from natural building materials.
- Stores CO₂: stores more carbon than is released during manufacture
- Moisture-regulating – reduces the risk of mould thanks to the high lime content
- Sound insulation up to 44 dB at 36 cm wall thickness
- Low flammability – reaction to fire class B-s1,d0 according to EN 13501-1
- Installation like conventional masonry – no special tools required Discover IsoHemp hemp blocks
System 2 of 5 · λ 0,040 W/mK
Gutex Thermoroom
The all-rounder for interior and exterior use
Gutex wood fibre boards made from Black Forest spruce and fir combine good thermal insulation performance with very easy installation. They can be sawn, stapled and bonded – and are suitable for external insulation (ETICS).
- Good λ-value (0.040) – efficient in little space
- High heat storage capacity protects against summer heat
- Vapour-permeable – no risk of condensation
- Renewable raw material: wood
- Easy application for professionals and DIYers Discover Gutex wood fibre
System 3 of 5 · λ 0,08 W/mK
Hessler Kalk-Dämmputz HP 9 SL
Ideal for listed buildings and older properties
Hessler HP 9 SL is a natural lime plaster with expanded glass aggregate that is applied directly to the masonry – no anchors, no frames, no substructure. The first choice when interventions in the building fabric are to be kept to a minimum.
- No cutting of boards: purely plastering work, applied quickly
- Suitable for listed buildings – looks like ordinary interior plaster
- Moisture-regulating and with a reduced risk of mould thanks to the high pH value of the lime
- Can be combined with clay plaster as a finish Discover Hessler insulating plaster
System 4 of 5 · λ 0.21 W/mK
Conluto expanded clay lightweight loam
Mineral filling and insulation
Conluto expanded clay light clay is a free-flowing fill material made from building clay and expanded clay. It is ideal for cavities, ceiling infills and lightweight timber-frame walls – wherever loose fill is a better fit than rigid boards.
- Simplest application: pour in, compact, done
- Produced regionally, very short transport distances
- Moisture-regulating thanks to the clay content
- Reaction to fire class B-s1,d0 according to EN 13501-1
- Combines excellently with other clay systems Discover Conluto light clay
System 5 of 5 · λ 0.036 W/mK
Gutex Thermoflex
Flexible for drywall construction and rafters
Gutex Thermoflex is the flexible wood fibre variant for drywall construction and insulation between rafters. The slightly springy boards clamp into the space between the rafters without adhesive – and deliver the best λ value in this round.
- Best λ-value (0.036) – maximum efficiency in the smallest space
- Clamp-fit without adhesive – very quick installation
- Natural material with high heat storage capacity
- Good sound insulation thanks to the wood fibre structure Discover Gutex Thermoflex
Frequently asked questions about natural insulation systems
Which system has the best thermal insulation value?
Gutex Thermoflex (λ = 0.036) and Gutex wood fibre (λ = 0.040) have low thermal conductivity. IsoHemp hemp blocks (λ = 0.071) combine higher thermal conductivity with load-bearing capacity and CO₂ storage, making them a durable all-round solution.
Which system is suitable for internal insulation in older buildings?
Hessler insulating lime plaster is the gentlest option – no substructure, no intervention in the building fabric, suitable for listed buildings. Gutex Thermoflex is the quickest solution for dry-lining installation.
Can I combine several systems?
Yes. Many projects use Conluto light clay as cavity fill and Gutex boards as insulation applied over the framing. Important: vapour diffusion must always become more open from the inside to the outside – never the other way round.
How do I calculate the quantity required?
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