A second group of materials includes highly transparent polycarbonate films in the cabin window. These are made of two sheets of Makrofol DE 1-1 polycarbonate film separated by a cushion of air. Other Bayer materials include films for covering structures, wing-covering fabric, and high-performance adhesive and coating materials in the cabin.
"Solar Impulse selected these materials because of their light-weighting capabilities," Rothe wrote. "For example, the polyurethane foam combines design freedom to form the faring and other complex components, as well as high insulation values at a very low density. Polyurethane parts were used where insulation is needed on the plane: cockpit cladding, motor cowling, and wing tips."
The HI-SIB will use the same materials groups: polyurethane foam, polycarbonate, and film and coatings. These will be further optimized, since the second plane needs to be even lighter. The cockpit's insulating foam materials (which also must deliver higher performance) are based on Baytherm Microcell and being co-developed with Solvay. "The material is better due to newly developed formulations, which allow for a significantly lower cell size," Rothe wrote. "These smaller cells make the polyurethane insulation properties even better and the density stays at a very low level. So the total weight should be lower." Another new development is a polyurethane resin for the carbon fiber composite.
For the HI-SIB, Bayer is providing and designing materials and structures. For example, it is handling the design of the cockpit shell. The windshield's sandwich structure will be similar to the HI-SIA's, but Bayer developed a new material that will reduce the likelihood of clouding from water condensation.
The second plane's coatings for all the exterior parts, especially the parts where no solar cells are located, are vital. They are extremely lightweight, allowing optimum protection for the films or textiles underneath. The coatings' "material properties will be the same, but no solvents will be used, which means the material is more ecologically friendly."