The joke is that blues music is traditionally associated with poverty, hardship, racism, and social inequality, while the scene is of wealthy white people in their opulant home. The joke is about how out of touch the privileged are.
It helps if you imagie the woman speaking in an upper class british accent, possibly after voicing her opinion about "those dreadful coloured people around the corner."
Its a good first step, but the r value of reflectix isnt nearly as much as foam board or fiberglass. Foam board has a reflective coating on the outside that will do the same thing (reflecting IR radiation). But if you have some lying around and it works, then it works.