The window is the thermal weak point of any home. Even in a well-insulated house, cold gets in most easily through the glazing. The reason is physical: glass conducts cold far faster than a wall, and the glazed area often represents 15 to 25% of the total wall surface of a room.
With single glazing, the heat loss is massive. The pane is cold to the touch, the indoor air cools on contact and sinks toward the floor, creating a constant draught of cold air along the window. This "wall of cold" in front of the window is something many households know well in winter.
With 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 drops. A 20-year-old double glazing no longer insulates the way it did on day one.
Patio doors and French doors pose an added problem: their large surface multiplies heat loss. A patio door 2 metres wide lets in far more cold than a standard window, even with good glazing.
On top of this come the draughts: worn seals around the frame, faulty sealing between the frame and the wall, infiltration under the French door. Cold does not only pass through the pane, it also gets around the window.
| Category | Density | Thermal gain | Sound reduction | Blackout |
|---|---|---|---|---|
| Standard thick curtain | 150 to 300 g/m² | 1 to 2 °C | 5 to 7 dB | 40 to 70 % |
| Mid-range | 300 to 500 g/m² | 2 to 4 °C | 12 to 18 dB | 70 to 90 % |
| High performance | 500+ g/m² | 5 to 7 °C | 18 to 25 dB | 95 to 100 % |
| Kurtens | 620 g/m² | Up to 7 °C* | 22 dB* | 100 %* |
The thermal curtain works on a simple principle: it creates a still layer of air between the cold pane and the inside of the room. This layer of air acts as a natural insulator and stops the cold from the pane spreading into the room.
The effectiveness of this barrier depends directly on the mass and density of the fabric. A standard decorative curtain (150 to 200 g/m²) is too thin and too light to hold air and block thermal exchange. Kurtens fabric weighs 620 g/m², three to four times heavier than a standard curtain. This mass creates a genuine textile wall that significantly slows the transfer of cold.
Measured result: up to 7°C of gain between the surface of the pane and the inside of the room*. In practical terms, if the pane is at 5°C on a winter night, the air on the room side behind the curtain stays around 12°C instead of dropping to the same temperature as the pane. The wall of cold in front of the window disappears.
The curtain also works the other way round. In summer, it stops outdoor heat and solar radiation from overheating the room, thanks to the 100% blackout that also blocks infrared. One curtain for both winter and summer. For the full technical details, see our made-to-measure thermal curtain collection.
*Figures from tests carried out under optimal conditions.
With single glazing, the thermal curtain is the first step to take. Replacing windows costs 500 to 1,000€ per opening and requires building work. The curtain installs in 30 minutes and delivers an immediate gain. It does not replace new glazing, but it significantly cuts the sensation of cold without touching the structure.
To compare the two approaches, read our article thermal curtain vs double glazing.
With old double glazing, the curtain compensates for the glazing's loss of performance. It adds an extra layer of insulation that extends the useful life of your windows until a possible replacement.
On a patio door or French door, made-to-measure is essential. The large dimensions (200 to 300 cm wide, 230 to 270 cm high) are not covered by any off-the-shelf curtain. The Kurtens configurator lets you order to the exact dimensions, up to 270 cm high.
In every case, the curtain should extend 15 to 20 cm beyond the window on each side and reach the floor. That is the condition for a complete insulating layer of air, so the cold cannot get around the fabric at the sides or the bottom.
The Kurtens curtain does not only insulate against the cold. The same 620 g/m² fabric also delivers 100% blackout and 22 dB of sound reduction*. Depending on your priority, explore our specialised collections: made-to-measure blackout curtain, made-to-measure soundproof curtain, or the blackout, thermal and soundproof collection that combines all three performances.
For large windows and patio doors, see our made-to-measure wide-width collection and our made-to-measure patio door curtain collection. To understand the science behind curtain thermal insulation, read our 2026 thermal guide.
Measure the area to cover: total window width plus 30 to 40 cm of overlap (15 to 20 cm on each side). Height from the top of the rod down to the floor. The curtain should skim the floor to eliminate cold leaks at the bottom. For a detailed guide, see our size guide.
Choose your finish from eyelets, pencil pleat or rod pocket. Our heading guide details the benefits of each system. The curtain weighs 620 g/m²: plan for a sturdy wall-mounted rod. Telescopic rods are not recommended for large windows.
7 colors are available: grey, off-white, cream, mint green, green, lilac and blue. They all deliver exactly the same thermal performance. The choice is purely aesthetic. See our color guide.
4 standard sizes are available (100x150, 150x230, 250x230 and 300x270 cm) if your windows match. Otherwise, the made-to-measure configurator lets you order to the exact centimetre, up to a maximum height of 270 cm. The Exact-Fit guarantee (€29.90) covers measurement errors: Kurtens remakes your curtain to the right dimensions.
Order your made-to-measure thermal anti-cold curtain
Frequently asked questions.
Is a thermal anti-cold curtain really effective?
Yes. The Kurtens curtain delivers up to 7°C of gain between the glass and the inside of the room*. It works by creating an insulating air layer thanks to its 620 g/m² fabric, three to four times heavier than a standard curtain. The condition: the curtain must extend 15 to 20 cm beyond the window on each side and touch the floor so the cold cannot get around it.
Does the anti-cold curtain also work in summer against the heat?
Yes. The thermal barrier works both ways. In winter, the curtain stops the cold from the glass entering the room. In summer, it blocks outside heat and solar radiation thanks to 100% blackout. One curtain for both seasons.
My home has single glazing. Is the curtain enough to insulate from the cold?
The curtain is the first step to take: it brings an immediate gain with no work and without touching the window. It does not replace a glazing upgrade, but it considerably reduces the feeling of cold in front of the window. For many single-glazed homes, it is the best efficiency-to-investment ratio before considering heavier renovation work.
What dimensions are best to properly insulate a window from the cold?
The curtain must extend 15 to 20 cm beyond the window on each side and touch the floor. If the curtain is too small, the cold gets around the fabric at the sides and bottom, and the insulation is compromised. This is why made-to-measure is recommended: every window has its own dimensions. See our size guide to measure correctly.
Does the curtain also insulate against noise?
Yes. The same 620 g/m² fabric that blocks the cold also reduces noise by 22 dB*. It is the triple performance: thermal insulation, 100% blackout and noise reduction in a single curtain. To learn more, see our made-to-measure soundproof curtain collection.
What is the difference between an anti-cold curtain and secondary glazing or an insulating film?
Secondary glazing and insulating film stick onto the glass and add a thin layer of insulation. The thermal curtain creates a thicker barrier (620 g/m² fabric + air layer) and requires no gluing or modification of the window. It installs and removes without leaving a trace. The three solutions are complementary, but the curtain also offers blackout and soundproofing.
What is the delivery time?
Allow 5 to 7 days for manufacturing and 5 to 10 days for shipping. Each made-to-measure curtain is made to your exact dimensions. Delivery is free in mainland France, Belgium, Switzerland and Luxembourg. The Exact-Fit guarantee (€29.90) covers measurement errors.
Check out our guides for a perfect result.
