My home has some very big 6 ft by 8 ft windows likely a big source of heat loss and is contributing to high heat bills. It would be too expensive to replace them with modern vinyl windows and the products themselves are of high quality, just old and made of some kind of metal, so not energy efficient.
I know a seamstress who makes custom blankets for a few hundred dollars each. They can fill with any material, cotton, goose feathers, etc. I could request they make blankets the size of the windows, but with added holes so they are supported by curtain rods. Would such a product have a big affect on stopping heat loss through the windows?