R-Value and U-Value: What Value Are They to You?

If you’ve never purchased or repaired windows, you might not know what you need when that time comes. It seems like there are countless window types to sort through. Comparing window ratings is a good starting point, but even then it’s not crystal clear. R-value vs U-value? Is one more important than the other? And what is a good score? Here we break down R-value vs U-value and help you figure out where to go from there. After all, a straightforward problem like warming your home should have a straightforward solution.

Building envelope air flow diagram: windows will have worse R-value & U-value than walls & roofs.

What Is R-Value?

R-value is a score given to a barrier – such as a wall, roof, or window – based on its ability to resist the flow of heat through it. Think back to elementary school when we learned about heat conductors and insulators. Can you recall copper as one of the best examples of a heat conductor? Heat passes through it easily. So copper would make a very bad wall. For your home’s “shell” (building envelope), you want something that resists heat transfer. The R-value (the ‘R’ stands for “resistance”) will tell you how well different barriers will resist that transfer.

Frozen copper pipe. Better resistance to heat transfer means a better R-value for a surface.

In the US, you will see R-values ranging from 0 to 66. Higher numbers mean better resistance to heat transfer. While R-values can be assigned to any surface of a building envelope – roof, ceiling, floor, wall, window – it is important to think about the role a surface plays in your home.

Walls are well-insulated and meant to protect against the outside elements. Windows should insulate, but also be able to open and let fresh air in. Windows should also be transparent for visibility and sunlight. For this reason, comparing the R-value of an insulated wall to the R-value of a window is not a good teller of insulation qualities. Compare the R-value of walls to that of other walls; compare the R-value of windows to the R-value of other types of windows.

What Is the Best R-Value for Windows?

A single-pane window will have an R-value of 1. 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 specialty windows that are highly insulated can reach an R-value of 5. This is great insulation, but the downside is the cost. Replacing multiple windows with these specialty windows will cost you thousands of dollars.

It is no secret that windows are the weakest spots in a building envelope when it comes to insulation. No windows will be able to insulate as well as the walls and roof of your home do. The aim is to increase their R-value and U-value as much as possible.

Performance Data Single-pane Window Double-pane Window Indow insert + Single-pane
Thermal Insulation (R-Value) R-1.0 R-2.0 R-1.87 94% of Standard Double-pane

What is U-Value?

U-value, or U-factor, is a score given to a surface based on how quickly it allows heat to pass through it. U-value can be thought of as the opposite of R-value. If R-value tells us of a surface’s thermal resistance, then U-value is a surface’s thermal transmittance. ‘R’ stands for resistance. For U-value, think of ‘U’ in circUlation, a word that has a similar meaning to “transmittance.”

But make no mistake: when it comes to winter insulation, a good U-value is given to a surface that transmits heat as slowly as possible. A good U-value does not indicate a surface quickly allowing heat to pass through it.

U-value scores typically range from 0.1 to 1. The lower the U-value, the better. A single-pane window has a U-value of about 1. This means it allows heat to pass through it quickly. A standard double-pane window has a U-value of about 0.5.

R-Value vs U-Value

While we say that R-value and U-value are opposites of each other, there are some differences that we should discuss. Traditionally, U-value was used for windows and R-value was used for the other surfaces of a building.

Sun through window. A difference in R-value vs U-value: U-value counts radiative & conductive heat.

R-value tells us how well a surface resists heat transfer. U-value tells us how quickly or slowly a surface allows heat transfer. Radiative heat from the sun has a much greater effect on windows than it does insulated roofs and walls, so that is taken into account with U-value. As a result, you can expect a window’s U-value to change based on time of year and time of day.

Calculating for R-value and U-value is easy. Dividing 1 by the R-value will give you the U-value:

R-value = 1/U-value

Dividing 1 by the U-value will give you the R-value:

U-value = 1/R-value

How Can You Improve Your Windows’ R-value and U-value?

If you have an historic home with original windows, replacement is not an option. It can hurt the historic value and many historic districts do not allow window replacements. Maybe you don’t have the ability to take on an expensive window replacement project. You can improve your windows’ R-value and U-value without replacement.

Window & Indow insert U-Value diagram: heat & cold air travel more slowly through acrylic than glass

Indow window inserts can be placed inside your window frames to improve the insulation of your window openings. When paired with single-pane windows, Indow inserts can improve the R-value to 1.87, or 94% of a double-pane window! With a double-pane window, the R-value will be improved even more. When paired with a single-pane window, Indow inserts will improve the U-value from 1 to 0.53. That is a huge improvement in insulation without the cost, time, or effort of a replacement project.

To see more performance data of Indow inserts and to learn about the various insert grades Indow offers, download our Product Data Sheet.

The Product Data Sheet also includes useful information on fit and egress compatibility with your windows.

Customer Reviews


4.49 Average 1423 Reviews logo

Charles T

Working with Indow has been a great experience from start to finish. They answered all our questions & guided us through the whole process. We ordered 15 inserts & they have reduced the Highway noise that we were experiencing after buying our house. A great product & innovative company.

Posted 1 day ago

Sue W

I live 20 feet from a busy road with lots of trucks. We almost didn't buy the house because of the noise. my house is the perfect candidate for indows. After installing them (myself. .. directions were so easy) we can barely hear any trucks noise at all. Indies live up to their claim and has made a huge difference.

Posted 2 days ago

Richard H

I am very pleased with the noise reduction and heat-trapping effects of my Indow inserts. I bought three small inserts as an experiment for the noisiest part of the house all year round, and where it's cold in winter. They have done beautifully well in sealing out both noise and heat. My only issue has been to get one of them installed perfectly straightly on one side, but it was done in a difficult location and isn't that important. They are also quiet expensive, but I may get a federal tax rebate on them.

Posted 6 days ago

Hee D

It could have been better if the pallet was collected after the delivery. Also the inserts are more beneficial for picture/fixed windows rather than open windows. The price of insert are expensive.

Posted 1 week ago

Larry S

I was pleasantly surprised how well the appearance after installation, perfectly clear, plus reduce the noise from the outside more than I expected. I would definitely recommend anyone looking for noise reduction to consider these. I will be purchasing more as time goes on, thank you Indow

Posted 1 week ago


Called about price $1000.00 For 2 small windows asked about energy savings? They said no guarantees depending on location and almost other factors, why would I spend that money w no guarantees

Posted 1 week ago

Christie R

It has cut down noise tremendously and is definitely more efficient with keeping our cooling in and heat out this summer.

Posted 1 week ago

William U

Indow is a trendsetter in eCommerce. They make the entire process of ordering, purchasing, and installing their product very easy for any walk of life; and, their communication processes are excellent. The inserts I purchased and installed were just as described. They are effectively blocking soundwaves, but not vibration, which was discussed during my initial call with an Indow Representative. I would recommend Indow window inserts to a friend.

Posted 1 week ago


Our window inserts have decreased road noise in our bedroom by 75 percent which we are very pleased with. The whole process was extremely simple and organized. Everyone we dealt with was professional and helpful. The inserts were simple to install and I would recommend to others.

Posted 2 weeks ago

Jeanne S

They make it easy to measure and install and it does reduce the noise as I live next to a busy highway. I am happy with the purchase.

Posted 3 weeks ago

Ivan L

We have a multi-story building construction next block that starts at 7 a.m. daily and a busy street a few blocks away. Before the insert was in place in our bedroom, we heard every piece of construction equipment there, including the obnoxious beeps from vehicles backing down in the lot, and all of the emergency vehicles passing by on the avenue. Now, this sounds like something happening twenty blocks away, barely noticeable. This is a huge quality-of-life improvement from day one of the insert installation.

Posted 3 weeks ago

Stan B

All fit as planned and are good

Posted 3 weeks ago

Cassie M

Overall very easy process from ordering to install. Was just hoping that the sound dampening would have been a little better.

Posted 3 weeks ago

Dan C

Effective and frequent communication from Indo Window starting with the order process, through production and post-delivery. The insert fit was excellent, fitting snuggly. The panel is quite effective in reducing noise. My wife was sleeping in the basement due to traffic noise. She is able to sleep in her bedroom again. Overall an excellent experience!

Posted 1 month ago

Lynett P

Great product. Arrived a bit dirty.

Posted 1 month ago