Mine's made with alminium so it's so cold in winter and no politicians have ever banned it yet, WTF JAPAN! RAGE QUIT!
I just use grey curtains lol (at least I assume this is what you're talking about?)
He is asking about the sash.
I think most buildings use either wood or metal for them.
Metal is more durable than wood, so I think it is better even if it means it is cold. Use curtains or something to separate the coldness from your living space.