Insulated Windows

I'm not talking about an operating system. I'm talking about the window in my room. My dad finally covered it with some plastic window material that helps keep heat from being lost at my window. My room already feels warmer. I tried explaining that one way I could tell that my window is where a lot of heat was being lost is by the amount of condensation on my window. He responded that all windows 'sweat' because of the change of temperature. I think that's bullocks because good windows don't sweat like pigs.