Thermal energy is stored as kinetic energy in the form of vibration, rotation, and translation. That k will depend on the makeup of the gas. Monatomic gas can't store any energy in rotation whereas diatomic and larger molecules can. (This is why humidity matters, water has three atoms and thus different thermal energy characteristics)

How much thermal energy ends up as kinetic energy in translation effects the proportion of T to speed of sound.

The storage also depends on temperature, how much energy goes into each degree of freedom (rot, trans, vib) changes with temperature but is fairly static around the human experience scale of things.