What Type of Spacer is Used. This is the first foray into the weeds of window components. The spacer is the part of the window that creates the gap between the two panes. The two panes and the spacer make up what is known as the “insulated glass unit” Or IGU. The spacer is important because it determines how long that IGU will maintain its seal. When the IGU sustains seal failure, then condensation occurs inside the IGU making it unsightly and diminishing its insulting property. From its inception through to today’s date, window spacers are typically metal, either aluminum or stainless steel. Metal spacers are being phased out in the industry because they conduct heat and fail in as short as six years. The optimum in modern spacers is the Super Spacer, a structural foam product. Its flexibility allows it to maintain its seal for the long haul, and as a material it does not conduct heat.