How to Choose Curtain Weight: A Complete Guide by Use
Curtain weight, expressed in grams per square metre (gsm), is the first criterion when choosing a curtain: it measures the density of the fabric and directly governs blackout, thermal insulation and noise attenuation. Below 300 gsm, a curtain stays decorative. From 500 gsm, it becomes genuinely insulating. The Kurtens curtain, at 620 gsm across three layers, blocks 100% of light*, holds back up to 7 °C of difference* and attenuates up to 22 dB*.
Choosing the right weight means starting from your need: a sheer or a mood curtain is happy at 100 to 250 gsm, a blackout or thermal curtain requires at least 500 gsm, and maximum performance sits above 600 gsm.
What curtain weight actually means
Weight is the mass of the fabric for one square metre. A 600 gsm curtain weighs twice as much, for the same surface, as a 300 gsm one. This density is not an aesthetic detail: it determines how much material light, heat and sound have to pass through. The denser the fabric, the more it blocks. That is the basic rule, and it applies to all three of a curtain's performances at once.
In acoustics, this principle has a name: the mass law. Each doubling of a wall's surface mass improves sound insulation by about 6 dB. A 600 gsm curtain therefore attenuates noise noticeably better than a 300 gsm one. The same reasoning applies to light and heat: density is the common lever. For the detail of this mechanism, see our article on weight versus the number of layers.
Table: what each weight is worth
Here is what each weight range really allows, from sheer to technical curtain.
| Weight | Curtain type | Blackout | Thermal / acoustic insulation | Use |
|---|---|---|---|---|
| 100 to 250 gsm | Sheer, light curtain | Low (filters light) | Almost none | Decoration, daytime privacy |
| 250 to 500 gsm | Mood curtain, semi-blackout | Partial (60 to 90%) | Low to moderate | Living room, ambiance, low-exposure windows |
| 500 to 600 gsm | Blackout / thermal curtain | Strong (close to 100%) | Real | Bedroom, insulation, comfort |
| 620 gsm (Kurtens) | Blackout thermal soundproof curtain | 100%* | Up to 7 °C* and 22 dB* | Maximum performance, all year round |
*Data obtained under optimal test conditions. Real performance depends on exposure, glazing and fitting.
Which weight for which need
The right weight depends on what you expect from the curtain. To dress a window and filter light without blocking it, a sheer of 100 to 250 gsm is enough. For a warm atmosphere in a living room, with a nice drape and partial blackout, aim for 250 to 500 gsm. To sleep in the dark, insulate against cold or heat, or reduce street noise, you need to pass the 500 gsm mark: below that, the insulating effect stays marginal. And to combine all three performances in a single curtain, it all happens above 600 gsm.
The most common mistake is choosing a curtain labelled "blackout" or "thermal" without checking its weight. A light fabric badged "thermal" will not insulate: only density makes the performance. Weight is the objective figure to ask for before any purchase.
Weight and drape: finding the balance
A high weight brings performance, but also a beautiful fall. A dense fabric hangs more regularly, forms clean folds and gives the curtain a refined look, far from the floaty appearance of sheers. At 620 gsm, the Kurtens curtain keeps a natural drape despite its density, because the three layers are assembled to stay supple. That is the advantage of a controlled weight: technical performance does not come at the cost of stiffness.
The only limit to anticipate: a heavy curtain needs a suitable rod. Above 500 gsm on wide spans, avoid telescopic rods and favour a solid fixing.
Why fitting matters as much as weight
A high weight only delivers its full value if the curtain covers the whole opening. A curtain that is too narrow or too short lets light, air and sound through on the sides, whatever its weight. This is why made-to-measure extends weight: a dense curtain, cut to the exact dimensions of the window with the recommended overlaps, removes leaks and truly exploits the density of the fabric. To size it well, see our guide on how to measure a made-to-measure curtain. The French agency ADEME, in its summer comfort guide, recalls that protecting your windows from solar radiation is the most effective way to keep a home cool in summer, which a dense, well-fitted curtain reinforces.
Kurtens weight: 620 gsm across three layers
The Kurtens curtain brings together three technical layers for a total of 620 gsm: a decorative fabric, a blackout membrane and a high-density backing. This assembly blocks 100% of light*, holds back up to 7 °C of difference* and attenuates up to 22 dB*, in a single curtain rather than three layered ones. Cut to measure to the exact dimensions of your window, it turns density into real performance. Configure yours in the custom curtains collection, or target a specific function: blackout, thermal or soundproof.
Frequently asked questions
What weight for a blackout curtain?
For real blackout, aim for at least 500 gsm. Below that, the curtain lets some light through. Total blackout, close to 100%, requires a dense, opaque fabric: the Kurtens curtain achieves it at 620 gsm across three layers, blocking 100% of light*.
Does a high weight make a curtain warmer in winter?
Yes. The denser the fabric, the more it limits heat exchange with the window. From 500 gsm, the thermal effect becomes real. The Kurtens curtain, at 620 gsm, holds back up to 7 °C of difference* and works as well against cold in winter as against heat in summer.
What weight to attenuate noise?
Sound attenuation follows the mass law: below 300 gsm the effect is almost nil; from 500 gsm it becomes noticeable. The Kurtens curtain, at 620 gsm, attenuates up to 22 dB* of the noise passing through the window. Weight is the first acoustic criterion, ahead of the number of layers.
Does a heavy curtain have a nicer drape?
Yes. A dense fabric hangs more regularly, forms clean folds and gives a refined drape. It is one of the advantages of a high weight, provided the layers stay supple, as on the Kurtens curtain at 620 gsm which keeps a natural fall despite its density.
What weight for a sheer curtain?
A sheer sits between 100 and 250 gsm. Its role is to filter light and preserve daytime privacy, not to insulate or black out. If you want blackout or insulation, you need a much higher weight, from 500 gsm upwards.
Does made-to-measure change the effect of weight?
Yes. A dense curtain only delivers its full value if it covers the whole opening. Cut to measure to the exact dimensions of the window, with the recommended overlaps, it removes light, air and sound leaks on the sides. Made-to-measure turns weight into real performance.
How do I find a curtain's weight before buying?
The weight should appear in the product specifications, in gsm. If it is not stated, that is often a bad sign: high-performance curtains display their density. Ask for the figure before any purchase, it is the most objective criterion to compare two curtains.
Key takeaways
Weight is the first criterion of a curtain, before colour, fabric or the number of layers. Below 300 gsm, the curtain stays decorative; between 300 and 500 gsm, it dresses and partly blacks out; above 500 gsm, it genuinely insulates; and from 600 gsm, it combines blackout, thermal insulation and noise attenuation. The Kurtens curtain, at 620 gsm across three layers, reaches 100% blackout*, up to 7 °C of difference* and 22 dB* of attenuation, cut to the exact dimensions of your window. Configure yours in the custom curtains collection.
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