Different kinds of Boundary (or Wall)

The categorization into system, control volume and isolated system is intimately associated with the kind of boundary or wall included. In a system, the border is resistant to matter, though can exchange energy with its surroundings in the type of heat or work. In a control volume, the boundary allows the transfer of mass and/or energy (in the type of heat or work); whereas in the situation of an isolated system, the boundary is impermeable to both mass and energy (either in the type of heat or work).
 
Three kinds of walls that divide the system from its surroundings are firm walls, diathermal walls and adiabatic walls:
(a) A firm wall will not allow a change in the volume of the system.
(b) A diathermal wall will allow the system to correspond thermally with its surroundings.
(c) An adiabatic wall is one that is resistant to thermal energy.