OT: [censored] thread, August, READ RULES IN TOP POST

[DevinLake]

Tin foil is used for a couple reasons. One, it blocks almost all sun light from getting in. Two, it reflects a lot of the radiation back out.

Black garbage bags will block a lot of the light. But, they will not have much of an effect on keeping your room from heating up. Not if they are inside. The radiation is still getting into the room, still heating the bags, which then convect heat to the rest of the room.

If you want to use passive controls in your house on windows to control heat, you use shutters (outside) in the summer and curtains/blinds in the winter.