Solid mass kills sound. When it comes to windows, you can use thicker glass. But the best innovation I have seen is to have a glass company make up, for you, a replacement insulated glass panel with differing thicknesses of glass. If you use thick glass for one and a less thick piece for the other, you get both heat and sound insulation. When glass vibrates, it does it best at certain freqencies. If both pieces of glass are the same thickness, they both resonate at the same harmonic. With different thicknesses, one glass doesn’t hand on its vibrations as well. Looks the same — works way better!