We had all our windows replaced with Polar Seal Polar Seal Royal Seal Vinyl Windows. We have 8 windows we had replaced which included a picture window with a center window and two side windows that are double hung. So this was quite a project but the house was 23 years old and still had the original windows which were pretty bad. These new windows have what's called a superspacer which is a structural foam spacer that insulates cold and warm. Normally thermopane windows use a metal spacer bar but this spacer works much better at warm and cold when you want each. The glass is also adaptable to the northern climates which is where we live in Michigan for the Low "E" glass helping to filter ultraviolet rays to help with cooling and heating and stops fading of carpet, furniture, drapes, etc. They are the great design that you can pull inside to clean and pop back into place. The other great thing is we were able to choose a color of vinyl visible from the outside which matched our painted garage doors and of course means we never have to paint around the windows again-yeah! The only downside is they have a border which is used to drain off water to the outside but means the kitty can no longer sit in the window as a flat surface comfortably so of course we had to add a shelf to each usable window for her to look out and oh-it's carpeted.