Low E4  If you have been shopping for windows or if it's time for a window replacement in your home, High-Performance™ Low-E4™ glass is for you. Get windows that stay cleaner, dry faster for easy cleaning and that have up to 99% less water spots*.   The new Low-E4™ glass reduces water spots up to 99%* and minimizes dirt build-up on the window when activated by sunlight. Low-E4™ glass saves time and money. It dries faster with fewer water spots and energy-efficient Low-E4™ glass also adds thermal protection to a home**.      High-Performance™ Low-E4™ glass reduces sound penetration and protects interior from damaging UV rays. During shipping and finishing, a removable film protects Low-E4™ glass from dirt or mortar. Low-E4™ glass comes with a 20-year limited warranty.   * exterior glass only, when activated ** A study of identical homes comparing Low-E to ordinary dual-pane glass showed 25% in savings on cooling bills. 10% on heating bills. Savings may vary geographically.