Mashi, which direction is MM's windows facing? At our last place, it was full west, so it was scorching hot but with the foil, it was cooler. Then i used black binbags and we smelled yucky plastic smell when there was sun, and that got Dh to move quickly to put the curtain rails up. It is leaking lights from above
so i might still have to add something like the easy blackout blinds.
Wait, if you get mildew, perhaps it is on the north side.