Sturdy, lightweight carbon foam has many structural and insulating applications in aerospace engineering, energy storage and temperature maintenance. Many materials, from graphene sheets to biomass such as banana peels, can be used to make these foams, but they are not stable, are costly to make or have varied inner structures that often cannot be adjusted.

Now, researchers from China's Harbin Institute of Technology report in the journal ACS Applied Materials & Interfaces a technique to produce such a carbon foam from super-toasted bread. Starting with a flour-based recipe, they mixed in yeast and water, then kneaded and baked the dough. A laboratory tube furnace under argon gas conditions then carbonized the product into a hard foam.

Researchers created a strong carbon foam out of bread, maintaining its original, airy pore structure. Image credit: American Chemical Society.The researchers, led by Yibin Li and Qingyu Peng, of Harbin's Center for Composite Materials and Structures, tested the foam using several spectroscopy methods and found it to be mechanically stiff, able to shield against electromagnetic interference and less flammable than current carbon foams. They also say that this foam’s inner pore structure could be tuned by changing the amounts of yeast and water, which would allow it to be used for a variety of applications.

The research team reports the foam's compressive strength at 3.6 MPa, while its density is 0.29 g/cm³ (compressive modulus can be 121 MPa). The electromagnetic interference (EMI) shielding effectiveness measurements (specific EMI shielding effectiveness can be 78.18 dB·cm3·g–1) indicate the foam can be used as a lightweight, effective shielding material. And, unlike ordinary foam structure materials, its low thermal conductivity (lowest is 0.06 W/m·K) and high resistance to fire may make it a candidate for commercial thermal insulation material, according to the researchers.

Overall, the researchers say their results demonstrate a promising method to fabricate an economical, robust carbon material for energy efficiency, environmental protection and industrial applications.