Key takeaways
- We read 297 thermal curtain listings on Amazon UK on 30 September 2026, 248 once colour and size variants sharing the same copy were merged. 150 say they save energy or cut heat loss. Not one of the 248 puts a number on it.
- Every percentage in those listings is about light. We call that the blackout proxy: a light-blocking figure sitting where a heat figure should be.
- The one independent test we found, for Historic England, measured heavy curtains cutting heat loss through a single-glazed sash window by 41 per cent.
- On our stated assumptions that is worth about £7.50 a window each winter with gas heating at the October 2026 cap, or about £22 with electric heating. The £10.34 Deconovo pair pays for itself inside two winters on that sum.
Closing the curtains at dusk is the oldest bit of heating advice there is, and it has a far better evidence base than most of what gets sold with the word thermal on it. With the energy price cap rising on 1 October 2026, thermal curtains are one of the busiest searches in Amazon’s home section. Hundreds of listings promise to keep the heat in.
We wanted to know what those promises are made of. So we read every listing on the first two pages of four searches, counted what each one actually says about heat, then found the independent measurement the listings never cite and worked out what a curtain is worth in pounds.
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Prices and specs last checked 30 September 2026 · next check 11 November 2026 · how we picked
The blackout proxy: 248 listings, no heat figures
On 30 September 2026 we searched Amazon UK for thermal curtains, thermal blackout curtains, insulated curtains and thermal door curtain, and read the first two pages of each. That gave 297 curtain listings. Many are the same curtain in a different colour or size with identical copy, so we merged those, leaving 248 distinct listings. For each one we read the title, bullet points, product facts, description and technical details.
| What the listing says | Listings | Out of |
|---|---|---|
| Thermal or insulated in the title | 193 | 248 |
| Claims to save energy, cut heating or reduce heat loss | 150 | 248 |
| Puts a number on heat saved or heat loss reduced | 0 | 248 |
| Gives a U-value, R-value, tog or thermal resistance | 0 | 248 |
| Cites a thermal test | 0 | 248 |
| Claims blackout | 218 | 248 |
| Triple weave construction | 112 | 248 |
| Foam backing or a coating | 46 | 248 |
| Fabric weight in grams per square metre | 20 | 248 |
| A thermal lining | 13 | 248 |
The headline is simple. 150 listings tell you the curtain saves energy or keeps heat in. None of the 248 says how much. Six mention testing, and none of those tests is about heat: they are about materials and harmful substances. Not a single listing gives a U-value, a tog or any other measure of how well the fabric insulates.
What the listings do have is percentages, lots of them, and every one is about light. “Blocks 85 to 95 per cent of sunlight.” “100 per cent blackout.” The Enhanced Living listing puts it most plainly: a bullet headed “ENERGY SAVING”, and the only figure under it is that up to 85 per cent of incoming light is blocked. We call this the blackout proxy: a light-blocking figure sitting where a heat figure should be. A fabric can stop light and still let heat through, so the proxy tells you nothing about the thing you are paying for in October.
What heavy curtains actually do: the Historic England test
There is a proper measurement, and it is not on any of these listings. In research for English Heritage, now Historic England, a Glasgow Caledonian University team (Chris Wood, Bill Bordass and Paul Baker) measured the heat loss through a traditional single-glazed timber sash window, then measured it again with various improvements in place. The window as found had a U-value of 4.3 W/m²K. With heavy curtains closed it was 2.5, a 41 per cent reduction in heat loss through the window. The report also notes the surface you feel from inside the room went from about 12°C at the glass to 21°C at the curtain, which is why a curtained window stops feeling like a cold draught.
Two limits on that figure. The report does not describe the curtains beyond “heavy”, so there is no fabric weight or lining specification to match. And the window was single glazed. Double glazing loses much less heat to begin with, so a curtain has less to save, and we have not found a comparable measurement for it.
What that is worth in pounds, at the October 2026 cap
Here is the arithmetic, with every assumption stated. Take a single-glazed window of 1.5 square metres, 20°C inside and 5°C outside. At a U-value of 4.3 it loses about 97 watts. With heavy curtains at 2.5 it loses about 56 watts. That is 40.5 watts saved while the curtains are closed.
Close them for 14 hours a night and that is 0.57kWh of heat a night. Ofgem’s cap from 1 October 2026 sets gas at 7.97p a kWh on average. Through a 90 per cent efficient boiler, which is our assumption, the saving is about 5p a night, or about £7.50 a window over 150 cold nights. If you heat with electricity at 26.32p a kWh it is about 15p a night, or about £22 a winter.
That makes the cheapest pair on this page, the £10.34 Deconovo, a payback of under two winters on one single-glazed window with gas heating, if it performs like the heavy curtains in the test. Nobody has measured whether it does, which is the whole problem. A heavier, lined curtain is the safer bet to get close to that 41 per cent.
Three things decide whether you get the saving. Close them at dusk, not at bedtime, because the heat goes out while the room is warm. Let them reach the floor or the sill so warm air cannot slip down behind them. And do not let a curtain hang in front of a radiator, because that sends the radiator’s heat up behind the fabric and against the cold glass. Curtains also do nothing for gaps round the frame; our draught-proofing guide covers those, and our guide to stopping condensation on windows explains why you should open them again in the morning.
If you would rather heat yourself than the room, our guides to USB heated gilets and rechargeable hand warmers show both cost about a penny to recharge at the October 2026 cap.
How we picked these
We took the 248 listings from the audit, dropped anything we could not price or add to a basket on 30 September 2026, and read the Amazon UK best sellers rank on each product page. Then we picked six that do different jobs: a cheap pair, a door curtain, a lined curtain, a separate lining for curtains you already own, a wide pair for patio doors, and a heavy velvet. Prices are the buy box on the day for the size and colour named. Sizes and construction are as each listing states them. We do not test.
| Curtain | Best for | Price, 30 Sep 2026 | Size | Construction | What it claims on heat |
|---|---|---|---|---|---|
| Deconovo triple weave, pair | Cheapest bedroom pair | £10.34 | 2 x 117 x 138cm | Triple weave | Energy saving, by keeping light out |
| PONY DANCE door curtain | Front or back door | £9.32 | 1 x 132 x 213cm | Triple weave | Reduces heat loss, no figure |
| Dreamscene thermal lined | Living room, lined | £28.99 | 2 x 168 x 228cm | Thermal lining | Reduces heat loss, no figure |
| Kinfolk Textile thermal linings | Keep your curtains | £19.99 | 2 x 46 x 54in | 3 pass lining, reflective coating | Keeps warm in winter, no figure |
| Enhanced Living Vogue, 90 x 90in | Wide windows and patio doors | £40.99 | 2 x 229 x 229cm | Triple weave | Energy saving, by blocking 85% of light |
| Woaboy velvet, pair | Heaviest fabric | £29.99 | 2 x 46 x 90in | Velvet | Makes no thermal claim |
The six we would buy
Deconovo thermal blackout curtains, eyelet, 46 x 54in pair
£10.34 for the pair on 30 September 2026 · 4.5 stars from 74,411 ratings · number 2 in Curtain Panels
The best-selling thermal curtain in our sample by a distance, and at just over a tenner for two panels, each 117cm wide and 138cm long, the cheapest way to put a layer of fabric between a bedroom and a cold window. It is triple weave, which means a dense three-layer weave rather than a separate lining, it has 4cm eyelets so it goes straight onto a pole, and it is machine washable.
The catch: the listing describes the fabric as lightweight, and its energy-saving line rests on keeping light out. That is the blackout proxy at work: nothing on the page says how much heat it holds in. At £10.34 you do not need it to do much, but do not expect it to match a heavy lined curtain.
PONY DANCE thermal blackout door curtain, 52 x 84in, single panel
£9.32 on 30 September 2026 · 4.5 stars from 28,577 ratings · number 4 in Curtain Panels
A door is a bigger, draughtier hole than most windows, and a single long panel across it is the cheapest fix there is. This one is 132cm wide and 213cm long, enough to cover a standard front door with overlap, triple weave, OEKO-TEX certified for harmful substances, and washable below 30°C. Pair it with a brush strip along the bottom of the door and you have dealt with both the gap and the glass.
The catch: it is one panel, so you need a pole or a door curtain rail above the frame, and on a door you open all day you will be pushing it aside every time. The listing says it helps reduce heat loss but gives no figure.
Dreamscene thermal lined eyelet curtains, 66 x 90in pair
£28.99 for the pair in burgundy on 30 September 2026 · 4.3 stars from 2,685 ratings · number 16 in Curtain Panels
A proper lined curtain rather than a single dense weave: a face fabric with a thermal lining behind it, which is the construction closest to what most people mean by heavy curtains. Each panel is 168cm wide and 228cm long, floor length for most living room windows, and the listing sensibly tells you to buy 1.5 to 2.6 times the width of the window so the curtains hang gathered rather than stretched flat.
The catch: only 13 of the 248 listings we read mention a thermal lining at all, and this one, like the rest, puts no number on it. The price quoted is for burgundy at this size; other colours and sizes are priced differently.
Kinfolk Textile thermal blackout curtain linings, 46 x 54in pair
£19.99 for the pair on 30 September 2026 · 4.5 stars from 835 ratings
If your curtains are fine but thin, you do not need new ones. A separate thermal lining hooks onto the back of an existing curtain and gives you the second layer. This pair is a 3 pass blackout lining with what the listing calls a solar reflective coating, and the hooks come in the box. The listing also says the drop is two inches shorter than the stated size, so the lining does not show below the curtain.
The catch: you need curtains with a heading tape the hooks can go into, so check yours before you order. The listing says the lining keeps your room warm in winter but, like every other listing in our sample, does not say by how much.
Enhanced Living Vogue thermal eyelet curtains, 90 x 90in pair
£40.99 for the pair on 30 September 2026 · 4.4 stars from 4,272 ratings · number 6 in Curtain Tiers
Two panels, each 229cm wide and 229cm long, which is the size you need for a bay, a wide picture window or a set of patio doors, where most of the heat in a room tends to go. It is a triple weave, dim-out rather than full blackout, and the listing says it blocks draughts as well as light and helps with noise. It comes in a long run of sizes if 90 inches is too much.
The catch: its headline energy claim is the clearest example of the blackout proxy we found. The bullet reads “ENERGY SAVING”, and the only number underneath it is that up to 85 per cent of incoming light is blocked. Light is not heat. Buy it for the size and the weight, not for that line.
Woaboy velvet curtains, 46 x 90in pair
£29.99 for the pair on 30 September 2026 · 4.5 stars from 1,362 ratings · number 36 in Curtain Panels
The one proper test we could find used “heavy curtains”. This listing never calls itself thermal. It sells on looks: a high-density velvet with metal grommets, two panels each 46 inches wide and 90 inches long, washable in cold water. We include it because a dense pile fabric hung floor length is the kind of heavy curtain the test used, and because it shows that the thermal label on the other listings is marketing, not a separate class of product.
The catch: because the listing makes no thermal claim, there is nothing to hold it to. It gives no fabric weight either, so “heavy” is our reading of the material, not a measurement.
Questions people ask
Do thermal curtains actually work?
Heavy curtains do. The best independent measurement we found, carried out for Historic England, recorded a 41 per cent cut in heat loss through a single-glazed sash window with heavy curtains closed, taking its U-value from 4.3 to 2.5 W/m²K. What no Amazon listing we read tells you is how close its own curtain gets to that: none of 248 gives a heat figure.
How much can thermal curtains save on heating?
On our assumptions, a 1.5 square metre single-glazed window, 20°C inside, 5°C outside and curtains closed 14 hours a night, heavy curtains save about 0.57kWh of heat a night. At the October 2026 gas cap of 7.97p a kWh through a 90 per cent efficient boiler that is about 5p a night, or about £7.50 a window over 150 nights. With electric heating at 26.32p a kWh it is about £22. Double-glazed windows lose less to begin with, so expect less.
Are blackout curtains the same as thermal curtains?
Not necessarily. Blocking light and holding in heat are different jobs. Of the 248 listings we read, 218 claim blackout, and every percentage they print is about light. A blackout figure is no guide to heat, which is why we call it the blackout proxy.
What makes a curtain thermal?
Weight, layers and fit. A heavy face fabric with a lining behind it traps a layer of still air, and a curtain that reaches the floor or the sill stops warm air slipping down behind it. Triple weave gives a dense single fabric, foam backing or a coating adds a layer, and a separate thermal lining can be added to curtains you already have.
Should thermal curtains cover the radiator?
No. A curtain hanging in front of a radiator sends the heat up behind the fabric and against the cold window, so the room gets less of it. If the radiator is under the window, curtains that stop at the sill are the better choice.
Do thermal curtains help with condensation?
They can make it worse at the glass. A closed curtain keeps the room warm but leaves the window colder, and moist air that gets behind it condenses on the glass. Open them in the morning and ventilate, and see our condensation guide for the rest.
Sources
- Historic England, Research into the Thermal Performance of Traditional Windows: Timber sash windows (Wood, Bordass and Baker, Glasgow Caledonian University, 2009). historicengland.org.uk, read 30 September 2026.
- Ofgem, Changes to energy price cap between 1 October and 31 December 2026. ofgem.gov.uk, read 30 September 2026.
- Amazon UK product pages for all 297 thermal curtain listings in the audit, read 30 September 2026.
Prices were read on amazon.co.uk on 30 September 2026 and change often, so treat them as a guide and check before you buy. The comparison table near the top pulls live prices from Amazon’s product feed, which can sit slightly off the price in the buy box. Look Into is a Whito Ltd publication. We earn a commission on some links to Amazon at no cost to you, and commission never changes what we recommend or the order we list it in.