What, a little more description would make an actual sentence. Put a couple sentences together and make an actual question.
While it might be more effective than a black wall, aluminum foil is not as reflective as you think. Most aluminum foil is only about 55% reflective, that is without wrinkles and creases. Once wrinkled, it loses all consistency, which can lead to hot spots and the overall reflectivity drops to a measly 35%. Compared to white paint (80% reflective) and Mylar (95%+ reflective), it's a terrible choice.
White paint works great, easy, and low-maintenance. Easy to replace... just paint over it!! easy to clean... just paint over it!!! Fucked up your wall? Just paint over it!!!