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Windows are the thermal weak point of a home. Even in a well-insulated house, cold enters most easily through the glazing. The reason is physical: glass conducts cold much faster than walls, and the glazed surface often represents 15 to 25% of the total wall surface of a room.
With single glazing, thermal loss is massive. The glass is cold to the touch, the interior air cools upon contact with it and descends towards the floor, creating a permanent cold draft along the window. This is the sensation of a "cold wall" in front of the window that many households experience in winter.
In old double glazing (installed before 2000), performance degrades over time. The insulating gas between the two panes gradually escapes, the seals age, and the airtightness decreases. A 20-year-old double-glazed window no longer insulates as it did on day one.
Bay windows and French doors pose an additional problem: their large surface area multiplies heat loss. A 2-meter wide bay window lets in much more cold than a classic window, even with good glazing.
To this are added drafts: worn seals around the frame, faulty sealing between the frame and the wall, and infiltrations under the French door. The cold doesn't just pass through the glass; it also bypasses the window.
| Category | Density | Heat gain | Sound attenuation | Concealment |
|---|---|---|---|---|
| Standard thick curtain | 150-300 gsm | 1 to 2°C | 5 to 7 dB | 40 to 70% |
| Mid-range | 300 to 500 gsm | 2 to 4 °C | 12 to 18 dB | 70 to 90% |
| High performance | 500+ gsm | 5 to 7°C | 18 to 25 dB | 95 to 100% |
| Kurtens | 620 gsm | Up to 7°C* | 22 dB | 100%* |
The thermal curtain works on a simple principle: it creates a layer of still air between the cold window and the inside of the room. This air layer acts as a natural insulator and prevents the cold from the window from spreading into the room.
The effectiveness of this barrier directly depends on the mass and density of the fabric. A classic decorative curtain (150 to 200 g/m²) is too thin and too light to retain air and block thermal exchange. Kurtens fabric weighs 620 g/m², which is three to four times heavier than a standard curtain. This mass creates a genuine textile barrier that significantly slows down the transfer of cold.
Measured result: up to 7°C gain between the window surface and the inside of the room*. Concretely, if the window is at 5°C on a winter night, the air on the room side behind the curtain remains around 12°C instead of dropping to the same temperature as the window. The feeling of a cold wall in front of the window disappears.
The curtain also works in the opposite way. In summer, it prevents outside heat and solar radiation from overheating the room, thanks to its 100% blackout that also blocks infrared rays. The same curtain for winter and summer. For complete technical details, see our made-to-measure thermal curtain collection.
*Data from tests carried out under optimal conditions.
For single glazing, the thermal curtain is the first measure to take. Changing windows costs 500 to 1,000€ per opening and requires work. The curtain can be installed in 30 minutes and provides an immediate gain. It does not replace a window change, but it significantly reduces the feeling of cold without touching the building structure.
To compare the two approaches, consult our article thermal curtain vs. double glazing.
For old double glazing, the curtain compensates for the loss of performance of the glazing. It adds an additional layer of insulation that extends the useful life of your windows while awaiting a possible replacement.
For a bay window or French window, custom-made is essential. Large dimensions (200 to 300 cm wide, 230 to 270 cm high) are not covered by any standard commercial curtain. The Kurtens configurator allows you to order to exact dimensions, up to 270 cm high.
In all cases, the curtain must extend 15 to 20 cm beyond the window on each side and touch the floor. This is the condition for the insulating air gap to be complete and for the cold not to bypass the fabric from the sides or from the bottom.
The Kurtens curtain does not only insulate against the cold. The same 620 g/m² fabric also offers 100% blackout and 22 dB sound attenuation*. Depending on your priority, discover our specialized collections: custom blackout curtains, custom acoustic curtains, or the blackout, thermal and acoustic collection that combines all three performances.
For large windows and patio doors, consult our made-to-measure wide curtain collection and our made-to-measure patio door curtain collection. To understand the science behind thermal insulation by curtains, read our 2026 thermal guide.
Measure the area to be covered: total width of the window plus 30 to 40 cm overlap (15 to 20 cm on each side). Height from the top of the rod to the floor. The curtain should brush the floor to eliminate cold drafts from below. For a detailed guide, consult our size guide.
Choose your finish from eyelets, heading tape, or rod pocket. Our fitting guide details the advantages of each system. The curtain weighs 620 g/m²: plan for a solid wall-mounted rod. Telescopic rods are not recommended for large windows.
7 colors are available: grey, off-white, cream beige, mint green, green, lilac, and blue. All offer exactly the same thermal performance. The choice is purely aesthetic. Consult our color guide.
4 standard sizes are available (100x150, 150x230, 250x230 and 300x270 cm) if your windows match. Otherwise, the custom configurator allows you to order to the nearest centimeter, with a maximum height of 270 cm. The Exact-Fit guarantee (€29.90) covers measurement errors: Kurtens remakes your curtain to the correct dimensions.
Order your custom thermal cold-insulating curtain
Frequently Asked Questions
Is a thermal cold-blocking curtain really effective?
Yes. The Kurtens curtain provides up to a 7°C gain between the window and the interior of the room*. It works by creating an insulating air pocket thanks to its 620 g/m² fabric, which is three to four times heavier than a classic curtain. The condition: the curtain must extend 15 to 20 cm beyond the window on each side and touch the floor to prevent cold air from bypassing it.
Does the thermal curtain also work against heat in summer?
Yes. The thermal barrier works both ways. In winter, the curtain prevents cold from the window from entering the room. In summer, it blocks outdoor heat and solar radiation with its 100% blackout feature. One curtain for both seasons.
My accommodation has single glazing. Is a curtain enough to insulate against the cold?
Curtains are the first step to take: they provide an immediate gain without any work or touching the window. While they don't replace a window replacement, they significantly reduce the feeling of cold in front of the window. For many homes with single glazing, this is the best efficiency/investment ratio before considering more extensive work.
What dimensions are needed to properly insulate a window against the cold?
Curtains should extend 15 to 20 cm beyond the window on each side and reach the floor. If the curtain is too small, cold air will bypass the fabric at the sides and bottom, compromising insulation. This is why custom-made curtains are recommended: each window has its own dimensions. Consult our size guide for proper measurement.
Does the curtain also block out noise?
Yes. The same 620 gsm fabric that blocks out the cold also reduces noise by 22 dB*. It's triple performance: thermal insulation, 100% blackout, and sound reduction in a single curtain. To learn more, check out our custom soundproof curtain collection.
What is the difference between a thermal curtain and double glazing or an insulating film?
Secondary glazing and insulating film are applied to the window pane and add a thin layer of insulation. Thermal curtains create a thicker barrier (620 g/m² fabric + air gap) and do not require gluing or window modification. They can be installed and removed without leaving a trace. All three solutions are complementary, but the curtain also offers blackout and sound insulation.
What is the delivery time?
Allow 5 to 7 days for manufacturing and 5 to 10 days for shipping. Each custom curtain is made to your exact dimensions. Delivery is free in metropolitan France, Belgium, Switzerland and Luxembourg. The Exact-Fit guarantee (€29.90) covers measurement errors.
Check out our guides for a perfect finish.
