Why some glasses carry better heat than others

Oxide glass — the type used in windows, jam jars, labware, and much more — is also a predominant material in electronics, where the material’s thermal conductivity allows it to transfer heat away from fragile components in displays and other components. Despite glass’s widespread use, scientists still lack a complete understanding of how exactly composition changes thermal conductivity, previously identifying three properties that could play a role: specific heat, which measures how much energy glass can store when it warms up; sound velocity, which measures how fast vibrations travel through the glass; and the average free path of phonons, which describes how far those vibrations can move before scattering. Sukenaga et al. clarified how these three properties affect thermal conductivity.

The team found that materials with higher sound velocity also tended to have higher thermal conductivity, and that glasses with higher specific heat tend to have phonons with a lower average free path. Despite these opposing trends, the product of these two parameters stays nearly constant across different glass compositions, suggesting an underlying balance in how glasses carry and store vibrational energy.

“This work contributes to understanding the principal rule for designing the thermal conductivity of glass materials,” author Sohei Sukunaga said.

For the study, the team prepared 13 types of silicate glasses with different compositions and experimentally evaluated thermophysical properties — such as thermal conductivity, sound velocity, volumetric specific heat, and the average phonon free path — at room temperature.

Future research will determine whether the sound-velocity relationship found in this study applies to systems other than silicate glasses and whether it holds across different temperature ranges.

Source: “Dominant role of sound velocity in the thermal conductivity of silicate glasses,” by Sohei Sukenaga, Bunta Ozato, and Hiroyuki Shibata, Applied Physics Letters (2026). The article can be accessed at https://doi.org/10.1063/5.0351403 .