Thanks for your kind words and interest.

The internal plaster has thickness, an extent perpendicular to to wall surface through which heat is conducted (in a simplified on-dimensional model). As such it thermal conductivity [W/mK] and thickness [m] are important for that model.

In contrast, the heat transfer between the internal wall surface and the air in the room is different and is characterised by some kind of thermal resistance [m^2 K/W]. This lumps convection and radiation all into one number.

I hope all this makes sense