There are about four major types of window spacers used today. One is the standard aluminum spacer. The second is the intercept spacer. The third is the super spacer and lastly there is the Steele spacer.

 Standard aluminum spacers are very inexpensive to manufacture. They are the highest conducting spacers made today and are commonly used in lower end windows. This spacer has a  high seal failure rate.  The intercept spacer is a three sided spacer the is shaped like a U. Since there is only three sides to the spacer instead of four, like in the first standard spacer, the theory is that heat and cold will transfer slower through the window. One problem this spacer commonly has is that it has a higher failure rate because since it has only three sides it moves slightly easier than the standard four sided spacer. As the window goes through cold and hot weather changes the spacer will have a slight chance of separation from the glass. The seal failure rate is about sixteen percent. The Super Spacer system is commonly sold as a better spacer system, it is made out of a foam and in theory since the is no metal in the spacer, the window will have a much harder time transferring cold and heat. The down side is that the system is attached by a beutel (glue)  to the glass and if the window experiences very warm temperatures than the spacer can pull away from the glass. One large windows that have direct heat the Super Spacer might start to dip down in the middle between the glass. This spacer has about a eight percent failure rate. Lastly the Steele Spacer. The spacer is made from Steele. Steele conducts only 300 British Thermal Units (BTUs) per hour. Aluminum spacers conducts 1416 BTUs per hour. From the start, Steele is far superior to aluminum. The Steele spacers are coming used in most wood windows and high end vinyl lines.  The failure rate is about one percent.