Center for Light and Environmentally-Friendly Structures ZELUBA®

Research project

“Designer in Lab”

Green Water – A floating utopia for the harbor city

The Fleete (canals) of Hamburg's inner city were once full of life. Today, they are mainly unused and lacking in vegetation. The designers Beate Kapfenberger and Martha Starke would like to breathe new life into the urban waterways. With the support of the Fraunhofer WKI, they are developing floating islands which can carry plants and which are made from a robust and lightweight bio-material. This consists of 100 percent renewable raw materials – including recycled balsa wood from wind turbines. Through this project, a new form of green space will be created in the city: valuable biotopes, recreational spaces and meeting places on the water.

The image collage consists of a photo with additional graphic elements. The photo shows the view into a Hamburg Fleet (canal) with the typical red-brick buildings at the water's edge. On the water are floating islands with plants and animals in sketched form.
© Design studio “morgen.”
Floating islands with plants should contribute towards the renaturation of Hamburg's vegetation-poor canals.
Drawing of a floating island. It consists of a round plate in which a plant, complete with substrate ball, is suspended.
© Design studio “morgen.”
The floating islands should be made entirely from renewable resources, including recycled balsa wood from wind turbines.

The floating elements are produced here at the Fraunhofer WKI using balsa-wood foam encased in natural-fiber-reinforced bioplastics. The balsa wood is derived from scrapped wind-turbine rotor blades. For the outer shell, we use a bio-based polymer on the basis of itaconic acid and increase the strength by means of flax fibers. The flax fibers are grown in Europe and exhibit excellent mechanical properties.

Thanks to the intelligent design of the floats, the plants are watered passively. In order to achieve the shape necessary for this purpose, we are testing production by means of vacuum infusion. This technology is used in industry to manufacture complex components from conventional fiber-composite plastic. The focus of our development is on adapting the bio-based polymer for this established manufacturing process. This concerns, amongst other things, the viscosity and the processing time as well as the formulation with different reactive diluents.

Starting in August 2021, seven floating islands will be created in the Bleichenfleet between the two bridges Michaelisbrücke and Ellerntorbrücke. They will be technically tested over the course of one year and will then continue to be used to revitalize the canals. The design and evaluation of the biotopes is being carried out with the support of the environmental organizations BUND Hamburg and NABU Hamburg.


Social relevance

The floating islands can improve the quality of both air and life in the city. Appropriate planting will provide food, reproduction and refuge biotopes for fish, birds, insects and other small creatures in high-density urban areas.

The project also serves society in a much broader context: The floating islands illustrate the performance capabilities of modern bio-materials. As eye-catching exhibits in public spaces, they emphasize that materials made from renewable raw resources can now meet the most stringent requirements and can be manufactured on an industrial scale. The project is therefore contributing towards raising awareness regarding sustainable material solutions and ensuring that they are used more routinely in product development in the future.

Simultaneously, we are creating a possibility for recycling discarded wind-turbine rotor blades. Their core consists of lightweight balsa wood. When the rotor blade has reached the end of its life, the balsa wood accumulates in large quantities as waste. At present, there are very few material recycling options.


Economic advantages

With the floating islands, new utilization possibilities arise for bodies of water as areas for experience and recreation. This could be interesting for the tourism, gastronomy and event sectors.

Companies that produce, process or utilize lightweight materials are provided with a new opportunity for the use of bio-based high-performance materials, thereby improving their eco-balance and market position.

For operators of wind turbines, a new recycling perspective is being opened up: The balsa wood from discarded rotor blades is being transformed from a waste material into a valuable raw material.  

Project partners

  • Design studio “morgen.” from Beate Kapfenberger and Martha Starke (concept and project management)


Original project title: Grünes Wasser – Eine schwimmende Utopie für die Stadt am Hafen

Funding body: Fraunhofer-Gesellschaft through its network “Science, Art and Design”

Duration: 1.3.2021 to 30.9.2021

Further information

Project website

Further informationen about the project can be found on the project website (in German).

Science, Art and Design

Fraunhofer promotes interdisciplinary projects between the natural sciences and the humanities. The goal: creative solutions for complex societal challenges.