Aerogel is the best thermal insulation material at ambient air pressure. Micro porosity is what makes Aerogel an efficient thermal insulator thanks to the Knudsen effect, ironically Aerogel is >90% air but the molecules are restricted from interacting as the silica pores are smaller than air molecules. Aerogel’s nano cell diameters are between 50-100 nm, which are small enough to limit air movement. When air molecules interact less with each other the heat flow is reduced. Convection and conductive heat transfer is limited because of the porosity of Aerogel, which also reduces radiated transfer thanks to effective scattering due to the large surface area, over 700 sq meters per gram.
Interestingly, Aerogel also has high permeability to air, a property that can be useful when properly managed. At low to medium pressure differentials the thermal efficiency is maintained by the Knudsen effect with little to no reduction. If, however, the differential increases, at some point bulk-gas-flow will occur with a larger reduction in thermal efficiency. Adding semi-permeable or air barrier wraps should be considered to manage this, adding a reflective surface would help even more.
- Thermal conductivity is between 0.012 – 0.016 W/m.K
- Heat capacity is 1000 J/kg/K
In this experiment, 6 cm of mineral-wool and 2 cm of Levron Aerogel Felt were tested under the same conditions. Ice cubes on mineral-wool and Levron Aerogel Felt melted approximately at the same time. Of interest is the increase in the melting rate as the mineral-wool’s water content increased. The melting rate of ice cubes on Levron Aerogel Felt remains constant. Mineral-wool and similar traditional insulators generally perform poorly when wet. Levron Aerogel Felt has a great advantage at this point because it is super-hydrophobic, the glass fibers never feel the water.
If new ice cubes were added to the same materials the mineral-wool sample would melt first.