Windows with high R values include double-glazed windows, triple-glazed windows, and argon-filled windows. Double-glazed windows have two layers of glass with a space in between, while triple-glazed windows have three layers of glass.
Triple-pane windows, in particular, offer the highest level of efficiency. They consist of three layers of glass, with two spaces filled with insulating gas. This design significantly reduces the loss of heat and the intrusion of cold, making them ideal for regions with extreme weather conditions.
In a cold climate a good U-factor for a window is between 0.17 and 0.39. (That's between R-6 and R-2.5). Lower is better with U-factor--the opposite of R-value, when higher is better. The low end of that range is only achievable with higher-quality triple-glazed windows--windows with three layers of glass.
On average, double-pane windows have an R-value of 3-3.7, while triple-pane windows have an R-value of anywhere between 5-8.
Understanding the R-value of windows
So what's a good window R-value? Standard ENERGY STAR insulated glass R-values are usually about 3. This is good, but the highest R-value windows go up to a rating of 7. If you want maximum energy savings, look for at least R-5 windows.
Triple-pane glass has an additional air space and third sheet of glass added, which makes this the most-efficient glass type.
A good U-value would be anything that meets Building Regulations or lower – currently set at 1.4 for existing dwellings (see below). European window manufacturers put more emphasis on U-values and have the lowest values of 0.80 on the market compared to the UK.
What's the difference between R-values and U-values? While R-value measures thermal resistance through a material, U-value measures thermal conductivity. U-value ratings generally range from 0.1 (very little heat loss) to 1.0 (high heat loss).
U-Factor: This is a measure of insulation, or how well a window or door keeps energy (heat) from escaping. The less heat loss through the window or door, the more energy efficient the window or door.
Thermablok® Aerogel is a revolutionary advancement in thermal technology offering the thinnest insulation available to prevent thermal and cold bridging. Classed as a Super Insulation, Aerogel has the highest insulation value of any known material with the lowest thermal conductivity value of any solid (0.015W/mK).
It is possible to over-insulate your house so much that it can't breathe. The whole point of home insulation is to tightly seal your home's interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers. That's when mold starts to grow.
Insulation ratings can be improved by adding more layers of insulation. You can mix the type and material of insulation too. For example, if your attic already has fiberglass insulation blankets installed, you can improve its R-value by installing blown-in cellulose insulation on top of the blankets.
Triple-pane windows cost homeowners an average of $1,000 but typically range from $400–$3,000 per window. See which factors will impact your total cost. Triple-pane windows consist of three glass panes with a gas-insulated space between each layer.
Fiberglass Frames
Fiberglass window frames are dimensionally stable and have air cavities that can be filled with insulation, giving them superior thermal performance compared to wood or uninsulated vinyl.
A good R-value range: Greater than R-5. A good U-value range: 0.20 – 1.20 according to energy.gov.
Vacuum insulated panels have the highest R-value, approximately R-45 (in U.S. units) per inch; aerogel has the next highest R-value (about R-10 to R-30 per inch), followed by polyurethane (PUR) and phenolic foam insulations with R-7 per inch.
A standard double-pane window will have an R-value of 2. While a single-pane window with an R-value of 1 does not offer great insulation, you get a much better picture of its performance by comparing it to a double-pane window than to an insulated wall.
Some of the traditional ways U-values can be improved are: Add a low-e coating. Use double- or triple-glazed IGUs. Use a noble gas, such as argon, in the cavity between lites of glass.
The U-Factor measures how well the window in- sulates. While the U-Factor can take any value, in general for windows it ranges from 0.20 to 1.20. The lower the U-Factor, the better the window insulates. The SHGC measures how much of the sun's heat comes through the window.
U-values measure how much heat is transferred through a window. A low U-value provides better thermal performance; a higher quality double glazed window usually achieves values around 1.6W/m2K whereas triple glazing typically achieves U-values as low as 0.8W/m2K.
Double- or Triple-Paned Glass
Double-paned windows offer significant soundproofing and are cost-effective, while triple-paned windows provide maximum noise reduction and energy efficiency. Consider the level of ambient noise and your insulation requirements when making this choice.
Select Andersen® A-Series windows are recognized as Most Efficient of ENERGY STAR® in 2025. Specific glass options apply.