In condensed matter physics and thermodynamics, energy transport through solid media relies on three primary micro-scale carriers: phonons (quantized lattice vibrational excitations), photons (electromagnetic radiation quanta), and electrons (charge and thermal transport particles). In conventional dense solids or micro-porous matrices, energy transport by these carriers follows classical continuum physics, such as Fourier's Law of heat conduction, Ohm's Law, and Maxwell's equations. However, when material pore diameters shrink to the nanoscale (1 to 100 nm), matching the characteristic Mean Free Paths (MFPs) of these energy carriers, continuum transport models fail. They are replaced by scale-dependent scattering, reflection, and confinement phenomena.

Aerogels—combining nanoscale solid frameworks with tortuous nanometer gas pores—provide a physical platform capable of tuning and decoupling the transport of phonons, photons, and electrons.

Regarding phonon transport control (governing the solid-phase thermal conduction component), thermal energy propagation occurs via lattice vibrational waves (phonons). Aerogel backbones are constructed from amorphous nanoparticles measuring only a few nanometers in diameter—a dimension smaller than the characteristic phonon mean free path in dense parent solids (several nanometers to tens of nanometers in amorphous silica). As a result, propagating phonons encounter boundary scattering events at inter-particle interfaces, causing reductions in phonon group velocity and effective mean free paths. This micro-scale confinement suppresses the solid-phase thermal conductivity component to one-thousandth that of dense silica glass. Concurrently, because pore diameters fall below the mean free path of ambient air molecules (approximately 70 nm), gaseous thermal conduction is suppressed due to the Knudsen effect, where gas molecules collide with pore walls rather than with each other.

Regarding photon transport control (governing radiative thermal transport and optical transmittance), the dimensions of the internal pores and solid elements lie near visible and infrared wavelengths. By engineering aerogel pore size distributions and density profiles, materials scientists dictate photon scattering and absorption behaviors across targeted spectral bands. For instance, aerogel networks maintain high optical transparency across the visible spectrum while suppressing radiative heat transfer in the mid-infrared region (3 to 8 $mutext{m}$) through the addition of infrared-absorbing or high-refractive-index opacifiers (such as $text{TiO}_2$ or carbon black), which introduce Mie scattering and spectral attenuation.

Regarding electron transport control (governing electrical conductivity and electro-thermal energy conversion), in conductive aerogels (such as graphene or MXene networks), the continuous three-dimensional framework provides long-range quantum percolation pathways for electron movement. By tuning backbone crystallinity and inter-particle contact resistance, engineers maintain electrical transport while suppressing solid-phase thermal conduction. This performance decouples the historical coupling between electrical and thermal transport encapsulated by the Wiedemann-Franz Law. Through the nanostructural confinement of these three energy carriers, aerogel architectures provide insights for energy transport control in condensed matter physics.