In solids, heat passes from one point to another through conduction In Liquids and gases, So, in an empty space or vacuum heat is transferred by
Thermal Conduction through multiple materials For situation (a): Heat can also be transferred, even across a vacuum, by radiation
The most efficient thermal insulation system is based on a vacuum layer (one or more if needed) enclosed by surfaces characterized by low emissivity coefficient
In solids, heat passes from one point to another through conduction In Liquids and gases, So, in an empty space or vacuum heat is transferred by radiation