When buying dual pane or even triple pane windows you will probably be given option of the type of tint. Most jobs we install now use Low E tint and our customers are very pleased. The feature I am speaking of now is how the window system is sealed. This is very important, especially on a long term basis. When dual pane windows are manufactured a seal is placed around the edges and between the panes. This seal is to keep out moisture or other contaminants. If the seal fails moisture can get in between the glass panes causing condensation and even mold. At C-thru Industries, they use the Enviro Sealed system which is tested to last 120+ years. This is superior to Butyl spacers, polysulfide, polyurethane or hot melt butyl by a very wide margin. If you want more information please have a look the video at http://youtu.be/pahBisvqExo. This is a YouTube post and is very helpful.