Getting ready for winter

Though the day time is warm, morning and night are already cold these days.
I get ready for winter. I was suggested to cover the window with plastic seat that helps to cut the cold air outside.it will reduce the electric cost not to waste the heat inside last year by a friend. But I couldn't find the useful products any more because of being sold out. So I plans to do it early before going cold and being sold out.
Regularly the electric fee rose more than 30,000 yen during the cold season. This year, I try to challenge the cost down of the fee by covering the window.
It will not certain that will really work to cut the energy cost. But it's good to be conscious about saving energy these days.