Natural insulation materials such as hemp and flax are getting more and more popular

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In modern construction, the good thermal and insulating properties of traditional materials such as reed and clay have almost been forgotten. In the 1990s, an entrepreneur from Baden-Württemberg rediscovered hemp as an insulating material and introduced it to Germany.

Hemp is not only a source of cannabis, but is also suitable for ropes and as an insulating material. For a long time, however, cultivation was prohibited and strictly regulated. However, the first relaxations were made long before the current plans of the traffic light government in the 1990s. And for Carmen Hock-Heyl, a carpenter’s daughter from Stutensee near Karlsruhe, this was practically her moment to become a “hemp rebel”, as various newspapers called it. She was actually a qualified doctor’s assistant and nurse.

In 1996, she set about developing an ecological insulating material made from hemp fibres, and seven years later she began producing and marketing “Thermo Hemp” in her own company with around 50 employees. At the urging of the then majority shareholder Alfred Ritter, who is behind the chocolate brand of the same name, she had to withdraw from the management of Thermo Hanf Hock GmbH & Co. KG in 2013.

Thermo hemp and insulating flax – the names say it all

But nobody could take away her environmental prize of 250,000 euros from the Federal Environmental Foundation. Incidentally, she received it together with the “electricity rebel” Ursula Sladek from the then Federal President Joachim Gauck. And with her departure from management, she was also able to devote more time to the interest group she founded, Naturfaser-Dämmstoffe.


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Her company, which now operates under the umbrella of HempFlax Building Solutions GmbH with Kingspan Insulation as the new majority shareholder, still exists, of course. The products include insulation and building materials made from “Thermo Hemp Combi Jute” with 66 percent hemp and 22 percent jute fibres and 4 percent soda as fire protection as well as clay, needle felt, stuffing wool and glass fibre fabric. Of course, Thermo Hemp or HempFlax is no longer alone in the field. Other suppliers include Hemplith, Hempwool and Isover. A company called Dämm Flachs is a programme in itself. There are also wholesalers such as Naturanum and associations such as the Fachagentur Nachwachsende Rohstoffe e.V. (Agency for Renewable Resources).

While hemp or flax prices used to be significantly higher than those for other insulation materials, the prices for jute insulation boards are now quite competitive at around €5.00 to €13.30, depending on the thickness. According to energieheld, the material costs for premium insulation boards in the attic amount to 33 and 53 euros respectively. Adding the installation costs, customers would therefore have total costs of 6,300 and 8,300 euros respectively for 100 square metres.

Why thermal insulation and good arguments for natural fibres

Thermal insulation is a very important building block for the energy transition and environmental protection and sustainability. According to UNEP, the United Nations Environment Programme, real estate is responsible for around a third of global CO2 emissions. Residential buildings account for the largest share of this. And Germany is far too dependent on energy imports to let the energy-efficient refurbishment required by the EU slide. As the Sparkasse has determined, roof insulation or covering costs around 225 euros per square metre, but promises energy savings of 30 percent, as does external wall insulation, which costs 160 euros per square metre.

However, many homeowners shy away from thermal insulation, often not so much because of the costs, some of which are generously subsidised by KfW and the like, but because they have heard that renovating with conventional insulation materials such as rigid foam or mineral wool can cause problems. This starts with the fact that they can trigger allergies, continues with possible pollutant emissions and extends to the risk of mould growth and the insulation materials as fire accelerants that are difficult to extinguish. And when it comes to the risk of mould in particular, natural fibres such as hemp or flax are often better suited, and apart from that, of course, they are also more environmentally friendly because they are renewable and sustainable.

Less suitable for “perimeter protection”

Natural insulating materials such as hemp, wood fibre, reed or flax are generally a little more expensive, but have the advantage that the houses can still breathe and they still offer very good thermal conductivity and sound insulation. With an average thermal conductivity of 0.039 watts per metre and Kelvin, hemp offers good protection against heat and cold and is also a good moisture regulator.


On the negative side, the fire protection is comparatively low, which Thermo Hemp wants to compensate for by adding soda. Another disadvantage is that, like all natural materials, hemp and jute insulation boards are not at all or only partially suitable for external or perimeter insulation. Insulation boards made of mineral wool or rigid foam are usually used here, but more and more foam glass gravel and granulates made of cork and cellulose are also being used.

What is even more effective, however, is external insulation with insulating vacuum. Vacuum insulation panels are practically copied from the thermos flask and, with a thickness of just two centimetres, achieve the insulation value of the 20 cm polystyrene panels that are otherwise often used. However, according to DasHaus, they cannot be cut to size and are also very expensive at 225 euros per square metre. A kind of air cushion between the house wall and the façade is often sufficient for façade insulation in order to keep mould, moisture, cold and heat outside. With an additional outer skin made of wood, natural insulating materials can also be installed as mats or in the form of stuffing hemp in an environmentally friendly and sustainable way.

Source cover picture: Adobe Stock / mattisi

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