This comes directly off the Hunter Douglas™ “We Make Green Beautiful” brochure. R-value is the measurement or the resistance to heat flow. A regular wall for a typical house has an R-value of around 19 whereas s typical double paned window only has a value of around a 2. Window covering such as some of the Hunter Douglas Duettes™ can add up to TRIPLE there R-value! This will be huge on your energy bill. If you are in a colder area of the county and you need to have that heater on regularly (more than half the year), you need a window treatment that adds at least 1 point of R-value but the more the better. When you choose a product for its insulating properties, be certain to specify that it be inside mounted and fully recessed in the opening in order to get maximum efficiency. If you can’t mount on the inside of a casement and have to go over the whole thing (outside the window), make plenty of overlap. Cold air between the shade and the glass can too easily go around the sides, edges and bottom which will greatly reduce the effective r-value of that window treatment.