Aerogel Insulation: From Mars to Historic Buildings

Aerogels are a group of porous solid materials that exhibit an impressive range of physical properties. Among them, they have the lowest thermal conductivity of any solid known, which makes them perfect for the deep cold of space travel—and also for winters in Scotland. In a four-year study on energy efficient heritage districts, EURAC teamed up with a Scottish aerogel technology company to demonstrate how aerogels could be the future of building insulation.

Space Wool

Elena Lucchi, a senior researcher at EURAC, studies the energy efficiency of buildings. Her job is to find ways of raising the thermal performance of Europe’s historic building stock to meet the objective of a carbon neutral Europe by the end of the century. “One of the objectives of EURAC’s building envelope research,” says Lucchi, “is to evaluate the energy efficiency of new building material technologies. Putting up exterior or interior wall insulation in historic buildings compromises their aesthetic value or useable space, so we work with industry to look at viable alternatives. Blown-in aerogel insulation is one of them.” Lucchi and her team are studying the thermal behaviour of an aerogel fibre insulation product manufactured in Scotland by construction technology innovator, A. Proctor Group (APG). Recent testing in EURAC’s lab has demonstrated impressive thermal performance results from this woollen material when it is blown into the cavity behind the lath and plaster of old stonewalled buildings. Called “Spacefill” by APG, the product consists of a polyester fibre mesh impregnated with silica aerogel.

Thermal Dead Ends

First discovered in 1930 by a Stanford University professor, aerogel is produced by removing the liquid content from a conventional gel with a special drying technique. The resulting product retains its solid structure, but loses 99 percent of its water mass. Picture a bowl of panna cotta. If you took that gelatinous dessert and baked it in an oven, all the water content would evaporate and leave a pile of powder. With aerogel, the water content is removed through a ‘supercritical’ drying process that leaves a solid matrix of millions of tiny pores. The more common aerogels are made from silica. Their pores are part of a three-dimensional network of infinitesimally small particles of silica. The branches of this network finish in many “dead ends,” making thermal transport through the silica arduous. And the pores themselves are so small—only 20 to 40 nanometres across—that air molecules cannot pass through them, making thermal energy transfer by convection extremely difficult. Put a blowtorch under a one centimetre tile of silica aerogel and you won’t be able to melt a chocolate bar sitting on its surface.

Scottish Masonry versus Modern Technology

The astonishing thermal performance of silica aerogel is what interests the consortium of 23 research institutions and industry partners involved in the Effesus project, which is winding up this year. The project is dedicated to increasing the energy efficiency of historical districts by developing new technological materials such as aerogel insulation, special brick mortars, reflective coatings and high-performance windows. EURAC dovetails nicely into the project with its extensive competence in evaluating the energy efficiency of historic buildings and their energy retrofits.

For the aerogel insulation experimentation, EURAC was tasked with creating a 1.5 m2 replica of a heritage-building wall, constructed in the traditional Scottish manner. Putting the wall into the lab’s climatic chamber, they measured its thermal performance with and without the aerogel insulation. They found the R-value (thermal conductivity) was four times lower with Spacefill—meaning that it performed twice as well as the traditional insulations. In another part of the study, other members of the consortium prepared a demo site in Glasgow. A section of a traditional tenement house wall (dating from around 1910) was retrofitted with the aerogel product. “The results are very encouraging,” Lucchi says, “and the product is likely to be marketed by APG. Before it can be sold, though, the wool will have to go through other assessments to measure the material’s life cycle and sustainability. APG doesn’t have a commercial price for it yet.”