Natural insulation materials like hemp and flax are growing in attractiveness
A female entrepreneur from Baden-Württemberg rediscovered hemp as an insulation material in the 1990s and introduced it to Germany.
At the end of 2023 we wrote here about hemp and flax as insulation materials and asked whether the old idea of the “breathing house” was making a comeback. Just under two years later, the answer has become clearer: support is in place, the market is growing quietly, and Germany’s best-known hemp plant has a new owner once again. High time for an update, my dear.
Natural insulation materials are never the loud part of a renovation. No one proudly shows guests the insulation panel in the attic. And yet it is precisely this invisible material that determines how a house feels in the height of summer, how high heating costs will be in winter, and whether the walls will still be dry after ten years. Anyone renovating to a high standard today thinks about this issue from the start rather than ticking it off as a mere formality.
- Hemp, flax, wood fibre and cellulose are considered the established natural insulation materials. Wood fibre and cellulose dominate, with hemp and flax together accounting for around ten percent of the natural segment.
- The major advantage: these materials regulate moisture, insulate sound and protect against summer heat far more effectively than thin mineral boards.
- 2025 funding: via the BEG, the BAFA offers up to 20 percent grants, and many cities add another 5 to 25 euros per square metre for natural insulation materials on top.
- In November 2025, the pioneering Thermo Hanf plant in Nördlingen became part of C-HempFlax Building Solutions, a joint venture between C-biotech and the HempFlax Group.
- The weak point remains fire protection and external insulation in the ground. Other solutions are still needed here.
From hemp rebel to industrial product
Carmen Hock-Heyl’s name is woven into the story of German hemp insulation. The trained medical assistant and nurse from Stutensee near Karlsruhe rediscovered hemp as a building material in the 1990s, just as cultivation was being cautiously liberalised. At the time, several newspapers dubbed her the “hemp rebel.” In 1996 she began developing an ecological insulation made from hemp fibres; by 2003 her own production under the brand Thermo Hanf was up and running with around 50 employees.
In 2013, under pressure from majority shareholder Alfred Ritter-founder of the well-known chocolate brand-she stepped down from the executive board. She kept the €250,000 environmental prize awarded by the German Federal Environmental Foundation, which she received together with “electricity rebel” Ursula Sladek from then-President Joachim Gauck. Instead of retiring, she redoubled her commitment to the trade association for natural-fibre insulation that she had founded.
An idea that started as an ecological outsider is now a fixed pillar of the industrial construction-materials market. That, in essence, is the real success.
New owners, same plant
The factory itself has changed hands since our first report. It operated for years under HempFlax Building Solutions, with insulation giant Kingspan in the background. Since 1 November 2025 the site in Nördlingen has belonged to C-HempFlax Building Solutions, a joint venture between Belgian construction specialist C-biotech (part of the Cordeel Group) and the Dutch HempFlax Group. It is Europe’s oldest hemp-insulation production line of its kind, and the new owners plan to expand capacity and broaden the range of bio-based insulation products.
The range is no longer a niche curiosity. Thermo Hanf Premium combines hemp fibres with reinforcing fibres and a dose of soda for fire protection; other variants add jute, blow-in wool and clay building boards. Competitors such as Hemplith, Hempwool and Isover are also in the mix, while flax is represented by brands like Dämm Flachs. Wholesalers such as Naturanum and industry bodies like the Agency for Renewable Resources round out a market that has clearly professionalised.
What natural fibres can-and cannot-do
The technical core hasn’t changed; it’s simply better documented. Hemp achieves a thermal conductivity of about 0.039 W/m·K, putting it on a par with conventional insulation. Yet what really affects living comfort is something else: natural fibres store heat more sluggishly, so attic spaces stay cooler longer in high summer than under thin mineral wool. They also regulate humidity and are far less prone to mould-an advantage that convinces many homeowners more than any datasheet figure.
It is often this very fear of mould and harmful substances-not price-that stops people from renovating. Rigid foam and mineral wool carry reputations for triggering allergies, off-gassing and burning stubbornly in fires. Natural fibres score here with a more honest feel-good factor. Their drawbacks remain fire performance (offset by additives such as soda) and suitability in the ground. For perimeter insulation around foundations, mineral wool, rigid foam or foam-glass gravel are still the go-to materials, supplemented by cork and cellulose granules.
Is it still worth it in 2025?
This is where the biggest changes have occurred. In the past, hemp and flax prices were significantly higher than those of conventional insulation materials, but today many natural-fiber boards are competitively priced depending on thickness. Even more important is the funding landscape. Through the Federal Funding for Efficient Buildings (BEG), the BAFA offers up to 20 percent in grants if the measure stems from an individual renovation roadmap. Cities like Munich, Hamburg, Hannover, and Freiburg add their own subsidies of between €5 and €25 per square meter specifically for natural insulation materials-sometimes stackable with the federal grant.
Behind this lies a larger picture. According to the UN Environment Programme (UNEP), buildings account for roughly one-third of global CO₂ emissions, with residential homes contributing the largest share. Proper roof insulation saves about 30 percent of energy according to Sparkasse estimates, yet costs around €225 per square meter. For anyone already renovating, the surcharge for natural fibers over mineral wool is smaller than many think-especially when municipal support kicks in. A similar material logic to the renaissance of linen in fashion is now playing out in construction: old natural fibers are being rediscovered because they age honestly.
Quick Answers
▸Are hemp and flax really more expensive than mineral wool?
Not across the board. Depending on board thickness, jute and hemp panels are now competitively priced. When you factor in municipal grants of €5-€25 per square meter and up to 20 percent BEG funding, the gap often narrows to a surcharge that’s justified by the comfort gains.
▸Don’t natural insulation materials burn more easily?
Pure natural fibers are indeed combustible. That’s why manufacturers add fire-retardant treatments, such as soda in Thermo Hanf. In underground applications and high-risk areas, mineral insulation still takes priority.
▸Do natural fibers really help against attic heat in summer?
Yes-and that’s their underrated advantage. They store heat more sluggishly than thin mineral boards, so the space below the roof warms up more slowly during peak summer. For converted attics in older buildings, this is often the decisive comfort factor.
▸Is Thermo Hanf still available?
Yes. The Nördlingen plant continues production under the new joint venture C-HempFlax Building Solutions, a partnership between C-biotech and the HempFlax Group, launched in November 2025. It remains Europe’s oldest facility of its kind and is slated for expansion.
If you’re weighing renovation options right now, don’t dismiss natural insulation as an eco-markup-think of it as invisible living quality you’ll feel every summer but never see. For more on how modern living is defined quietly rather than loudly, read our piece The Apartment That Needs No Proof.
