I have double pane clear windows now and the heat in Texas is brutal. I hate the looks of the solar screens so have checked into the low-e glass. I found a local company who can replace some of my windows and they gave me a choice of cardinal low e squared, or guardian PP2 I think they call it. While investigating windows, I found so much as far as seals and gas, and did ready up on guardian and cardinal. Cardinal seems slightly better for our climate but I could be wrong. I have aluminum windows already so am getting the inserts replaced which is quick and easy. They told me they use spacers and the frame and seal the 2 glasses but don't use any argon or any type of gas inbetween, just air. Is this important or does it matter? I want to do a section at a time and since the one area already needs windows, that is easy. However I want to get the best efficiency possible. Thanks for any info.