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A thermal curtain works by creating a still layer of air between the fabric and the glass. It is this layer of air, not the fabric alone, that forms the insulating barrier. For this air layer to stay still, the curtain must cover the window perfectly: no gaps at the top, at the bottom, or on the sides.
A standard-size curtain always leaves spaces around the window. Cold air seeps in through these openings and cuts insulation by 30 to 50%. A made-to-measure thermal curtain, configured to the exact dimensions of your window, eliminates these thermal bridges and maximizes the temperature gain.
To combine thermal insulation with total blackout (100%), explore the made-to-measure blackout thermal curtain collection, two levels of performance in the same 620 g/m² fabric.
| Category | Density | Thermal gain | Sound attenuation | 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 %* |
Double glazing works around the clock, day and night, with the openings closed. The thermal curtain steps in where the glazing alone is not enough: at night when temperatures drop, on weekends and during absences, and in summer to block direct sunlight.
The two solutions are complementary. A home with double glazing and Kurtens thermal curtains combines the benefits of both: the glazing handles the constant exchange, the curtain reinforces insulation at critical moments.
What the curtain adds on top of double glazing:
- A still layer of air trapped between the fabric and the glazing, naturally insulating
- A block against summer sun rays that the glazing alone cannot provide
- Partial soundproofing to complement the thermal insulation
To go further, read our complete guide to choosing a thermal curtain or our thermal curtain vs double glazing comparison.
Contrary to a common belief, the thermal curtain is not only a winter solution. Its effectiveness works two ways depending on the season.
Winter: the high-density fabric creates a barrier against the cold air radiating from the glazing. Hung floor to ceiling, it stops convection.
Summer: closed during the day on the sunny side, it reflects and absorbs the sun's rays before they pass through the glazing. The effect is especially marked on south- and west-facing windows in the afternoon.
A thermal curtain loses a significant part of its efficiency if the dimensions aren't right. Thermal bridges form exactly where the fabric doesn't cover:
- The side gap: cold air slips in through the uncovered edges
- The floor gap: natural convection circulates cold air under the curtain
- The insufficient width: the window edges stay exposed
At Kurtens, our standard sizes are designed to cover the most common windows with the recommended thermal overlap. If your window is unusual, the made-to-measure option lets you enter your exact dimensions: side overlap of 15 to 20 cm on each side, adjusted floor drop, height configured to your ceiling. In both cases, an optimal fit is the condition for the 7°C* gain.
Need help measuring? See our size guide. For large windows, explore our made-to-measure wide-width collection.
*Under optimal installation and test conditions.
Frequently asked questions.
Does a thermal curtain really make a difference?
Yes. Tests measure a gain of up to 7°C* in a room with a correctly fitted Kurtens curtain. This gain is especially noticeable at night in winter and during the day facing the sun in summer.
*Under optimal installation and test conditions.
What's the difference between a thermal curtain and an insulating curtain?
When we talk about thermal insulation, both terms describe the same function: limiting heat exchange through the windows. A thermal curtain is an insulating (thermal) curtain; the distinction is semantic, not technical.
Is a thermal curtain effective against heat in summer?
Yes, that's one of its two functions. Closed during the day on a sunlit exposure, it blocks the sun's rays before they pass through the glass and heat the room.
Should a thermal curtain touch the floor?
Ideally yes. A 2 to 3 cm drop onto the floor eliminates the low thermal bridge through which cold air seeps in. That's why it's important to choose the right size, or to opt for made-to-measure if your height is unusual.
Is a thermal curtain also soundproof?
Kurtens decided to develop a 3-in-1 thermal curtain that is blackout, thermal and soundproof, while still letting in light. So your curtain gets all 3 qualities.
What temperature gain do you get with a thermal curtain?
A Kurtens thermal curtain can create a 7°C* gain between the glass surface and the inside of the room. This gain depends on the fabric density, the insulating lining and above all the fit to the exact dimensions of the window.
*Data from tests carried out under optimal conditions.
Which curtain blocks the cold?
A high-density thermal curtain with an insulating lining is a very effective way to block the cold at your windows. Kurtens curtains offer up to 7°C* of thermal gain, combined with 100%* blackout and 22dB* of sound reduction, made to the exact dimensions of your windows.
*Data from tests carried out under optimal test conditions.
How do you install thermal curtains correctly?
For maximum insulation, follow these principles: mount the rod as high as possible above the window (ideally at the ceiling), extend the curtain beyond the window frame on each side (10 to 15 cm minimum), make sure the curtain touches the floor or comes as close as possible depending on the drop you want, and close the curtain completely at night. During the day, open the curtains on sun-facing windows to benefit from the solar gain.
Is a made-to-measure thermal curtain more effective than a standard-size curtain?
Yes. A standard-size curtain leaves gaps around the window through which cold air seeps in. These leaks cut insulation by 30 to 50%. A made-to-measure curtain, configured to the exact dimensions of your window, eliminates these thermal bridges. That's the difference between a curtain that "decorates" and a curtain that truly insulates.
How much does a Kurtens thermal curtain weigh?
The Kurtens fabric has a density of 620 g/m2. A 150 x 230 cm panel weighs around 2.1 kg. A 300 x 270 cm panel weighs around 5 kg. This high weight is what gives the curtain its insulation performance. Plan for a sturdy rod with a minimum diameter of 28 mm and fixings suited to your wall type.
