Why are double window frames less cold permeable than single window frames?

This question is about outdated wooden frames. A single window frame is when there is only a layer of glass between the street and the room. If it’s cold outside, single glass, due to thermal conductivity, also quickly becomes cold and cools the air in the room. There is air in the double frame between the glasses, which has poor thermal conductivity, so the double frame is less cold permeable.