The cattail – an insulating material with real promise

Research in focus May 2013

Sometimes, taking a look at nature can inspire the best ideas – or, if you’re a researcher from the Fraunhofer Institute for Building Physics IBP, it can present smart solutions to many a structural problem. So when researchers from the working group for moisture management came to take a closer look at the cattail (Latin name Typha) they discovered that this aquatic and wetland plant is ideally suited for use as an insulation material.The natural resource can be recycled without difficulty, features solid insulating properties and “is already one of the most cost-efficient solutions for restoring timber-framed buildings,” says engineer Theo Großkinsky as he explains the advantages of this renewable insulation material.

Cattail plants can be found almost anywhere in the world and are also native to Germany, though they are mainly found in the Danube delta. The color of the flowers is brown and resembles smoke. In Greek, Týphe means plant.

The thick, reed-like foliage of the cattail plant can grow up to five meters long and is ideal for use as an insulation material – as Fraunhofer researchers found out for themselves when they teamed up with the engineer who made the discovery, Werner Theuerkorn. When made into panels, this foliage shows a thermal conductivity of 0.055 W/mK. The value expresses how many watts of heat energy are transported through a material per meter per degree Kelvin. The smaller the number, the better the insulating properties of the material. In comparison, the thermal conductivity of pure copper is 401 W/mK, and between 0.032 and 0.035 W/mK for glass or mineral woll and foams. In contrast to other insulation materials, Typha boasts significant load-bearing capacity and a high level of stability in addition to its insulating properties. “A unique combination!” declares Großkinsky.

The stability displayed by Typha panels stems from the production process used to make them, which was developed by Fraunhofer IBP researchers in collaboration with Theuerkorn. Großkinsky explains the production process – which uses comparatively little energy – as follows: “The leaves are sorted, cut with parallel blades and shortened to the specific length required for the foreseen application. Once cut up, the desired quantity of particles is taken and put into a mixer, where they are sprayed with a predetermined amount of magnesite adhesive. The particles, now covered with adhesive, are then put into a mold, where they are compressed according to requirements using a hot pressing technique.” Afterwards, the panels still have to be dried out for a few days before they can finally be used in construction. “In spite of the high stability of the panels following drying, they can easily be worked using standard tools,” stresses the research scientist.
“There are also other advantages to using Typha,” explains IBP team leader Dr. Martin Krus. “As an aquatic plant, it is extremely resistant to fungal attack, as well as offering good prerequisites for a good level of protection against fire and noise.” The material also stands out thanks to its vapor permeability and capillary action. This specific set of properties makes Typha seem almost predestined for use as a base material in the production of highly insulating building materials that are subject to high loads.
The restoration of a timber-framed house in Nuremburg gave researchers the opportunity to confirm the cattail’s desirable properties. In this instance, a listed building needed to be repaired and stabilized while retaining the typical timbered house look. Typha was selected for use in the project due to its solid insulating properties and stability. The innovative restoration was funded by the German environmental foundation Deutsche Bundesstiftung Umwelt (DBU) and the Bavarian State Office for the Preservation of Historic Buildings and Monuments. The fact that the material is easy to work with meant that it could be fit trimly to the crooked walls. Cartridge applicator guns were used to apply Typha grout to fill in joints and cracks in the wood, making the walls draftproof. The panels were directly plastered over using a particularly vapor permeable mixture of tuff sand and lime. Readings taken by Fraunhofer IBP over a period of 18 months show that Typha proved to be a particularly suitable choice of insulation material in this instance.
However, it’s not just its insulating properties and stability that speak for the use of Typha. Another big advantage gained by cultivating the cattail plant is that this would lead to the regeneration of fens that have been drained long ago for use as agricultural land. This is also the conclusion reached by German environmental foundation DBU’s study “Growing the cattail plant on fenland”, conducted under the direction of the Technische Universität München. Not only were the fens returned to their natural state, they also play a part in trapping carbon dioxide. “The drainage of fens leads to the release of up to 40 tons of CO 2 each year,” explains Krus. With CO 2 emissions standing at around 804 million tons per year in Germany alone, dealing with the issue by growing Typha would mean a step in the right direction, reckons the researcher. “Growing Typha could allow us to make a considerable contribution to protecting our environment.”
The amount of space needed to grow the cattail was also less when compared with a sector such as forestry. Natural, single-crop agriculture currently yields around 15 to 20 tons of plant dry matter per hectare each year. This is enough to produce around 150 to 250 cubic meters of building material. In comparison, a hectare of coniferous forest currently only yields around a fifth of this dry bulk.
Since the cattail plant brings together such an array of positive qualities, Fraunhofer IBP and the inventor of the insulating panels, Werner Theuerkorn, are currently on the lookout for a manufacturer who would also be capable of producing the panels in large quantities for use in the construction sector. Clearly, this is an instance where taking a look at one’s surroundings has paid off – for man and nature.

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