Egg Crate Foam

[Sir Terrence the Terrible]

I am having a hard time finding some egg crate foam. Would the egg crate foam that is used for a bed mattress work as good? I am wanting to use it in a window to both block the light and cover up around an window air unit in my bedroom.

Try thick black felt fabric instead. Its more attractive, will dampen some high frequency reflections around that air conditioning unit, and it will do a better job of blocking the light.