Among insulating window coverings cellular shades are the ones with a real rating system behind them, so the claim is more than a sales line. The honeycomb fabric traps pockets of air between the room and the glass, which slows heat moving through the window when the shade is down. DOE's Building America Solution Center says they can save energy in winter by adding insulation and in summer by blocking solar heat. How much depends on your window, your climate, how well the shade fits, and whether it is actually closed when it matters.
What the honeycomb actually does
A window loses heat in a few ways. Warm room air touches cold glass, cools, sinks and pulls more warm air in behind it. Heat also radiates from the room toward the cold pane, and some moves straight through the glass and frame.
A cellular shade puts a layer between the room and that cold surface. Each cell is a small pocket of air held in place by fabric. Still air is a poor conductor of heat, which is the same idea behind most insulation. A double-cell shade stacks two rows of pockets, and some fabrics add a reflective or blackout layer inside the cell.
The shade does not make the window better. It adds a second, removable layer in front of it, and only while it is down. Raised, it does nothing.
That is the honest frame for everything below. A cellular shade is an attachment to a window, not a replacement for one. DOE's Building Technologies Office calls this whole product class "window attachments," along with blinds, roller shades and storm windows.
Is a cellular shade "insulation"?
In the everyday sense, yes. It slows heat flow. But it is not insulation the way your attic is, and it helps to know why.
Attic insulation sits in place all year, sealed behind drywall, with no moving edges. A shade hangs in a room. It has gaps at the sides, top and bottom. Air can move around it, and it is only doing its job when someone lowers it.
So a shade can make a cold window feel less cold and cut some heat loss through the glass. It cannot stop air leaking in around the window frame, and it does nothing for the walls, attic or basement.
If your house feels drafty, check where the air is really coming from before you buy shades. A smoke pencil test for air leaks will show you whether the draft is at the window or somewhere else. Often the bigger losses are in the attic, which our guide to where the air leaks actually are walks through.
How much do insulating window coverings cellular shades save?
We will not give you a percentage, and here is why.
The savings from a cellular shade depend on variables we cannot see from here:
- Your existing window. A shade in front of old single-pane glass has more to improve than one in front of a newer double-pane window with low-E glass.
- Your climate. Heating-dominated and cooling-dominated homes benefit in different ways.
- The fit. Gaps at the edges let room air circulate behind the shade.
- How you use it. A shade left up on a winter night saves nothing that night.
- How many windows, and how much of your heat loss is through them.
Published studies do report figures, but they come from specific test houses and conditions. Our site does not quote a savings percentage that is not tied to your own house. A DIY home energy audit is the better way to see whether windows are a big share of your loss in the first place.
What we can point you to is a rating that compares products on the same test: the AERC label.
The AERC label: the one number worth reading
The Attachments Energy Rating Council (AERC) rates, labels and certifies window attachments, including cellular shades. DOE's announcement of the first rated window coverings, dated May 1, 2020 and read on September 27, 2026, says DOE's Building Technologies Office and Lawrence Berkeley National Laboratory helped establish AERC and developed the simulation models and test procedures behind it.
AERC's own guide to reading the residential label, read the same day, describes two main ratings:
- Cool Climate rating: potential energy savings when it is cooler outside and you run the heat.
- Warm Climate rating: potential energy savings when it is warmer outside and you run the air conditioning.
AERC says any product rated above zero on either can save energy compared with using no window attachment at all. Each product category has its own maximum possible rating, so compare shades against other shades, not against storm windows.
The label also lists U-factor, solar heat gain coefficient, visual transmittance and air leakage. If you have read an NFRC window label, those will look familiar.
Fit matters as much as fabric
Two shades with the same fabric can perform very differently once they are hung. The main difference is air movement around the edges.
Inside mount vs outside mount. An inside-mount shade sits within the window frame. An outside-mount shade covers the frame and a bit of the wall. Either can work. What matters is how small the gaps are at the sides and top.
Side channels. Some cellular shades can be fitted with tracks along the sides. They close the edge gap that lets room air slip behind the shade. Ask whether the product you are looking at offers them, and whether the rated product on the AERC label included them.
The bottom rail. Here there is a trade-off. DOE's Building America Solution Center notes that when an interior insulating shade is closed, the glass behind it gets colder, "potentially allowing condensation or frost to form." It suggests leaving the bottom rail about half an inch above the sill so a little air moves across the pane.
That is the honest limit of a tighter fit. The more a shade isolates the glass, the colder that glass gets. If you see water or frost on the window behind a closed shade, lift the rail slightly and look at your indoor humidity.
Using the shade so it actually helps
A shade saves nothing while it is rolled up. DOE's Building America Solution Center guide to window attachments, last updated July 26, 2023 and read on September 27, 2026, gives simple guidance:
- In winter: keep attachments open when the sun is shining on the window, to let in solar heat, and closed at night and on cloudy days to reduce heat loss.
- In summer: close them during the day and open them at night.
That is all it takes with a manual shade. Motorized and automated shades are a separate topic we do not cover here. AERC's label shows a separate, improved rating for products that are automated.
The same DOE guide points readers to the DOE-supported Efficient Window Coverings website, which compares types of window attachments on thermal, visual, functional, installation and durability criteria. It is a useful step before you look at brands.
How to compare cellular shades without a sales pitch
We have not tested any cellular shade, so we will not name a winner. Here is how to compare the options you are quoted.
- Ask for the AERC rating. Ask for the Cool Climate and Warm Climate ratings of the exact product, fabric and configuration you are being quoted. If there is no rating, you have no independent number to compare.
- Match the rating to your climate. In a cold climate, the Cool Climate rating matters more. In a hot one, the Warm Climate rating does. In a mixed climate, look at both.
- Compare like with like. Single cell vs double cell, light-filtering vs blackout, inside mount vs outside mount. Each changes the result.
- Ask about side channels. And whether the rated product included them.
- Check the cord design. If young children live in or visit the home, choose cordless or inaccessible-cord designs.
- Fix the bigger holes first. If your attic is under-insulated or leaky, that work usually comes before window coverings. Our guide on why you should air seal before you insulate explains the order.
FAQ
Do cellular shades really insulate?
They add a layer of trapped air between the room and the glass, which slows heat flow while the shade is down. DOE's Building America Solution Center describes multi-layer honeycomb cellular shades as providing added insulation in winter and blocking solar heat in summer.
Are double-cell shades better than single-cell?
A second layer of cells adds more trapped air, but the only fair comparison is the AERC rating of the specific products. Compare their Cool Climate and Warm Climate ratings rather than the cell count alone.
Can cellular shades cause condensation on windows?
They can. DOE's Building America Solution Center notes that a closed insulating shade lets the glass cool, which can allow condensation or frost. It suggests leaving the bottom rail about half an inch above the sill.
Are cellular shades a substitute for new windows?
No. A shade helps only while it is down and does not stop air leaking around the frame. It can be a lower-cost step for a window you want to keep, but it does not change the window itself.
What does an AERC rating of zero mean?
According to AERC, a product rated above zero on its Cool Climate or Warm Climate rating can save energy compared with no window attachment. The higher the number relative to the category maximum on the label, the better it performed on the test.