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A thermal curtain works by creating a still air gap between the fabric and the window pane. It is this air gap, not the fabric alone, that forms the insulating barrier. For this air gap to remain still, the curtain must perfectly cover the window: no gaps at the top, bottom, or sides.
A standard-sized curtain systematically leaves gaps around the window. Cold air infiltrates through these openings and reduces insulation by 30 to 50%. A custom-made thermal curtain, configured to the exact dimensions of your window, eliminates these thermal bridges and maximizes temperature gain.
Performance per tissue density: what the figures say
| 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%* |
Double glazing works continuously, day and night, with windows closed. The thermal curtain comes into play where glazing alone is not enough: at night when temperatures drop, on weekends and during periods of absence, 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 permanent exchanges, and the curtain reinforces insulation at critical moments.
What the curtain adds in addition to double glazing:
- A layer of still air trapped between the fabric and the glass, which is naturally insulating
- A blocking of solar rays in summer that glass alone cannot provide
- Partial sound insulation in addition to thermal insulation
To go further, consult our complete guide to choosing a thermal curtain or our comparison thermal curtain vs double glazing.
Contrary to popular belief, thermal curtains are not just a winter solution. Their effectiveness is twofold depending on the season.
Winter: the high-density fabric creates a barrier against cold air radiating from the windows. Hung from floor to ceiling, it prevents convection.
Summer: when closed during the day on the sunny side, it reflects and absorbs solar rays before they pass through the glazing. The effect is particularly noticeable on south and west exposures in the afternoon.
A thermal curtain loses a significant part of its effectiveness if the dimensions are not adapted. Thermal bridges are created precisely where the fabric does not cover:
- The lateral gap: cold air rushes in on the uncovered sides
- The gap at the bottom: natural convection circulates cold air under the curtain
- Insufficient width: window edges remain exposed
At Kurtens, our standard sizes are calculated to cover the most common French windows with the recommended thermal overhangs. If your window is unusual, the custom-made option allows you to enter your exact dimensions; a lateral overhang of 15 to 20 cm on each side, an adjusted drop to the floor, and height configured according to your ceiling. In both cases, optimal installation is the condition for a 7°C* gain.
Need help with measuring? See our size guide. For large windows, discover our made-to-measure wide curtain collection.
*Under optimal installation and test conditions.
Frequently Asked Questions
Does a thermal curtain really make a difference?
Yes, tests measure a temperature increase of up to 7°C* in a room with a properly installed Kurtens curtain. This increase is particularly noticeable at night in winter and during the day facing the sun in summer.
*Under optimal installation and testing conditions.
What is the difference between a thermal curtain and an insulating curtain?
If we're talking about thermal insulation, then both terms refer to the same function: limiting heat exchange through windows. A thermal curtain is an insulating curtain (thermal); the nuance is semantic, not technical.
Is a thermal curtain effective against the heat in summer?
Yes, that is one of its two functions. Closed during the day on a sunny exposure, it blocks solar rays before they pass through the glazing and heat up the room.
Does a thermal curtain have to touch the ground?
Should a thermal curtain touch the floor? / Ideally, yes. A 2-3 cm drop to the floor eliminates the low thermal bridge through which cold air seeps. That's why it's important to choose the right size or opt for a custom-made curtain if your ceiling height is unusual.
Is a thermal curtain also soundproof?
Kurtens has decided to develop a 3-in-1 Thermal curtain that is blackout, thermal, soundproof and also bright. Your curtain will therefore have all 3 virtues.
What is the temperature gain with a thermal curtain?
A kurtens thermal curtain can create a 7°C* gain between the glazed surface and the interior of the room. This gain depends on the density of the fabric, the insulating lining, and especially on the precise fit to the window's dimensions.
*Data from tests performed under optimal conditions.
Which curtain to block the cold?
A high-density thermal curtain with an insulating lining is a very effective solution for blocking out cold at windows. Kurtens curtains offer up to 7°C* of thermal gain, combined with 100%* blackout and 22dB* sound attenuation, made to the exact dimensions of your windows.
*Data from tests carried out under optimal test conditions.
How to properly install thermal curtains?
For maximum insulation, follow these principles: install the rod as high as possible above the window (ideally on the ceiling), extend the curtain beyond the window frame on each side (10 to 15 cm minimum), ensure the curtain touches the floor or comes as close as possible depending on the desired drape, and close the curtain completely at night. During the day, open the curtains on sun-exposed windows to benefit from solar gain.
Is a custom-made thermal curtain more effective than a standard-sized curtain?
Yes. A standard size curtain leaves gaps around the window through which cold air infiltrates. These leaks reduce insulation by 30 to 50%. A custom-made curtain, configured to the exact dimensions of your window, eliminates these thermal bridges. This is the difference between a curtain that "decorates" and a curtain that truly insulates.
What is the weight of a Kurtens thermal curtain?
Kurtens fabric has a density of 620 g/m2. A 150 x 230 cm panel weighs approximately 2.1 kg. A 300 x 270 cm panel weighs approximately 5 kg. This high weight is what gives the curtain its insulation performance. Provide a sturdy curtain rod with a minimum diameter of 28 mm and fixings suitable for your wall type.
