Sonicism 12 Pack Pyramid Sound Proof Foam Panels with Self-Adhesive, 12" X 12" X 1" Acoustic Foam Panels of High Density, Soundproof Wall Panels Fast Expand, Sound Absorption and Decoration (Black)

In addition to what the other helpful people have said, I have some sound deadening panels in my window and it does a fairly good job with noise. I have them glued to a sheet of cardboard that is cut to the size of my window so that I can theoretically take it out. But I just leave it in and don't worry about the look or sunlight.