What is the R-value?

R-value- is the rate of heat flowing through a material or the metric U-value.  The higher the R-value number, the more effective the window is in reducing cooling and heating costs. R-values can be shown in a two primary formats: The R-value can be shown in SI, or System International, units of Kelvin meters squared per Watt, or in imperial units, square foot degrees Fahrenheit hours per British thermal unit.   You need to know what R-value you are looking at is measured in as Si unit of 0.78 watt per meter kelvin [W/(m·K)] translates to 5.41 inch per hour square foot degree Fahrenheit [BtuIT·in/(h·ft2·°F)]. Calculator for conversion 

Window R-values typically range on scale from 0.13 for single 3mm glass pain to 0.78 for double glassed window. Typically, there are two R-values associated with windows. One value is for the glass itself and the other is for the entire window unit, including the frame. The type of glass, frame and window sash can affect the R-value.

Why You Should Value R-value

Quite simply, R-value measures how well a material reduces energy (heat) gain or loss. It’s a measure of thermal resistance, used most commonly in building and construction. To put it in perspective, sprayed foam wall insulation has an R-value between R-2+ and R-4+, depending how thickly it’s applied. Your windows have an R-value, too. Double glazed glass is around R-0.26 – roughly 9% as resistant to heat transfer as your walls.
Understanding R-value allows you to shop wisely so you can decide on the most efficient and cost-effective household resources. The higher the R-value, the more energy you save. Energy saved is money saved!

So, About Those Windows…

Now that you’re an R-value pro, you might be thinking about how much less insulating your windows are than your actual walls. You might be correct in assuming more that 50% pf your energy bill is flying out the window, or how your living room turns into an oven in the summer. But don’t give up hope! There are energy-saving solutions to these sheets of glass we’ve grown to know and love.

Cellular window shades are designed with R-value in mind: the honeycomb-shaped fabric uses air pockets to slow the movement of thermal energy. Air happens to be a fantastic insulator (a 20mm pocket of air has an R-value of .13!). Between the air pockets of the shade’s honeycomb cells and the insulating shade material itself, energy loss doesn’t stand a chance.
Energy is always trying to expand. In the winter, the warm air inside your home naturally moves toward and out your windows, so that it can expand into cold, open air. In the summer, outdoor heat tries to make its way back inside your cooler home. Cellular window shades work as a barrier against both types of energy transfer, so you save year-round