The U-Value is a measure of an IG's ability to block heat transfer - lower values of U indicate better insulating performance, and
equate to higher R values.
Below are just a few examples of U and R values with various glass make-ups using 1/8" glass and ½" airspace where applicable:
Item Single Pane Double Pane IG Double Pane with lowE Triple Pane IG |
"U" 1.0 .49 .36 .32 |
"R" 1.0 2.04 2.78 3.13 |