Every material has fundamental material properties that determine their energy performance like conductivity, resistance, and thermal mass. Knowing these terms will help you chose the right materials to improve heat flows.
A Trombe wall is a system for indirect solar heat gain that is a good example of thermal mass, solar gain, and glazing properties used together to achieve human comfort goals passively. It consists of a dark colored wall of high thermal mass facing the sun, with glazing spaced in front to leave a small air space.
Thermal mass is a material's resistance to change in temperature. Objects with high thermal mass absorb and retain heat. Thermal mass is crucial to good passive solar heating design, especially in locations that have large swings of temperature from day to night.