How to Create an Efficient Vinyl Window
Energy efficient vinyl windows are made with modern glass, super spacers and gas fills. The chambered frames are insulated for strength as well as for insulating efficiency.
Low emmissivity glass often referred to as Low E squared or LOW E2 greatly increases the efficiency of todays modern windows and may in fact be required to meet the local building codes. It acts to reflect heat ionto a home in the winter and reflect heat away in the summer, hence the nick name "Smart Glass."
Argon or Krypton gas fills further increase efficiency by reducing the rate of heat transmission between the panes. There are some fears that the argon gas fills may leak out over time reducing the efficiency of the window frames. If that is a concern, then you need to consider using Super Spacers.
Super Spacers were originally designed to keep gasses in by making a solid fill seal around the perimeter. The foam used with the sealing system had an unexpected benefit. The system further reduced heat loss and condensation. Now, years later, the seal system is known for its' energy efficiency and not for preventing gas loss.
There is a lot of technical information available on the web at sites like NWHI.net and others.