Thermal curtain vs. double glazing: an honest comparison of performance and costs
Double glazing reduces heat loss by 50 to 80% compared to single glazing. High-density multi-layer thermal curtains reduce it by 20 to 30%, with a measured gain of up to 7 °C*. In pure thermal performance, double glazing is superior. But it costs 5 to 10 times more, requires a professional, and is not always feasible (tenants, co-owners, listed buildings).
The real answer: the two solutions are not competing, they are complementary. Double glazing addresses the window, while the curtain addresses the space between the window and the room (heat, light, noise). This guide compares the two based on concrete criteria.
The numbers: compared thermal performance
To compare objectively, we need to talk about thermal resistance. The Ug coefficient (or Uw for the entire window + frame) measures heat loss through glazing: the lower it is, the better the insulation.
| Solution | Thermal Performance | Gain vs. Single Glazing | Estimated Savings |
|---|---|---|---|
| Single Glazing | Ug approx. 5.8 W/m².K | Reference | Reference |
| Standard Double Glazing | Ug approx. 2.8 W/m².K | Reduces losses by about 50% | 150 to 300 euros/year |
| High-Performance Double Glazing (argon) | Ug approx. 1.1 W/m².K | Reduces losses by about 80% | 250 to 450 euros/year |
| Classic Thermal Curtain (single lining) | Adds R +0.1 to +0.3 m².K/W | Reduces losses by 10 to 20% | 30 to 80 euros/year |
| High-Density Multi-Layer Thermal Curtain (620 g/m²) | Up to 7 °C measured gain* | Reduces losses by 20 to 30% | 60 to 150 euros/year |
Double glazing is clearly superior in pure thermal performance. This is an undeniable fact. But a raw comparison doesn't tell the whole story, because it ignores the context in which each solution is used: cost, installation, versatility, and the housing situation.
Savings are estimated for a 60 to 80 m² dwelling with 5 windows, electric heating at 0.22 euros/kWh. Windows account for 10 to 15% of a dwelling's heat loss, according to ADEME.
*Data from tests conducted under optimal conditions with a Kurtens 620 g/m² curtain.
Cost: a very different value for money
| Criterion | Double Glazing | Custom Thermal Curtain |
|---|---|---|
| Cost for a standard window | 300 to 800 euros (supply + installation) | 80 to 200 euros |
| Cost for a complete dwelling (5 windows) | 3,000 to 10,000 euros | 400 to 1,300 euros |
| Installation | Mandatory professional, 1 to 2 days | Do it yourself, 5 minutes per window |
| Authorization required | Yes (co-ownership, listed building) | No |
| Return on investment | 10 to 30 years (before aid) | 3 to 7 years |
| Lifespan | 20 to 30 years | 10 to 15 years |
| Transportable (moving) | No, stays with the dwelling | Yes, disassembles in 30 seconds |
| Additional functions | Thermal insulation only | Thermal + 100% blackout* + acoustic 22 dB* |
For a tenant, the calculation is simple: invest 400 to 1,300 euros in thermal curtains that can be installed without authorization and taken along when moving, rather than asking the landlord to invest 5,000 to 10,000 euros in double glazing.
When the thermal curtain outperforms double glazing
There are concrete situations where a thermal curtain is objectively the best option, regardless of budget:
- Tenants: The only reversible and transportable window insulation solution. No landlord will forbid you from installing a curtain. And you can take it with you when you leave.
- Windows already double-glazed: A multi-layer curtain adds an extra layer of insulation. The gain is less than with single glazing, but still noticeable (2 to 4 °C of additional comfort), especially on north-facing or wind-exposed windows.
- Multiple problems (cold + noise + light): Standard double glazing insulates against cold but blocks neither noise nor light. A Kurtens curtain offers up to 7 °C of thermal gain*, 22 dB of sound attenuation*, and 100% blackout* simultaneously. To achieve these three performances with glazing, reinforced acoustic triple glazing with shutters would be needed, representing an investment of 1,500 to 3,000 euros per window.
- Large bay windows: The largest heat loss surfaces in the dwelling. A 3 m² bay with standard double glazing (Ug 2.8) loses as much heat as 10 to 15 m² of insulated wall. A custom thermal curtain precisely sized for the bay eliminates thermal bridges.
When double glazing remains essential
In some cases, a thermal curtain is not enough, and double glazing is the right answer:
- Owners with single glazing and available budget: Replacing with double glazing is the best long-term investment. Financial aid significantly reduces the cost: MaPrimeRénov' covers 40 to 100 euros per window depending on income, and CEE (Energy Savings Certificates) add 30 to 80 euros per window. The return on investment is 5 to 15 years on heating savings.
- Windows in poor structural condition: Failing seals, rotten frames, defective closures. No curtain will compensate for massive air infiltration. The problem is structural and requires replacing the joinery.
- New construction or full renovation: Double glazing (or even triple glazing, required by RE2020 in certain configurations) is a standard that naturally fits into the overall project.
The ideal combination: double glazing + thermal curtain
The question "thermal curtain or double glazing" is actually poorly posed. The two solutions are not competing; they are complementary.
High-performance double glazing reduces heat loss by 80% compared to single glazing (Ug from 5.8 to 1.1-2.8 W/m².K). A multi-layer thermal curtain adds a thermal resistance of R 0.3 to 0.6 m².K/W. Combined, the system approaches the performance of a lightweight insulated wall (U from 0.5 to 0.8 W/m².K for the entire glazing + curtain). The cold wall effect disappears, light is controlled, and noise is attenuated.
In recent homes equipped with good double glazing, the curtain primarily acts as a comfort regulator: total blackout for the bedroom, sound attenuation for rooms facing the street, reinforced thermal protection for large glazed surfaces exposed to the sun in summer or cold in winter.
To go further in choosing your textile insulation, consult our complete guide to choosing your thermal curtain. And to understand why dimensions matter as much as fabric, discover our article on how to insulate your windows against the cold without major work.
Summary: which solution for your situation
| Your Situation | Recommended Solution | Estimated Budget |
|---|---|---|
| Tenant, single glazing | Custom thermal curtain (only realistic option) | 80-200 euros/window |
| Tenant, double glazing | Thermal curtain for comfort (blackout, acoustic, thermal) | 80-200 euros/window |
| Owner, single glazing, budget available | Double glazing + thermal curtain (complete solution) | 380-1,000 euros/window |
| Owner, single glazing, limited budget | Thermal curtain while waiting for double glazing | 80-200 euros/window |
| Owner, recent double glazing | Thermal curtain for blackout, acoustic, and comfort | 80-200 euros/window |
| Large bay windows | Custom thermal curtain (gain over large area) | 150-350 euros/bay |
Whatever your situation, a high-density multi-layer thermal curtain improves the comfort of your home. Double glazing addresses the window. The thermal curtain addresses your daily comfort: conserved heat, controlled light, attenuated noise. Discover our custom curtains available in 7 colors with free delivery in mainland France, Belgium, Switzerland, and Luxembourg.
*Data from tests conducted under optimal conditions.
Frequently Asked Questions
Can a thermal curtain replace double glazing?
No. Double glazing reduces heat loss by 50 to 80% (Ug from 5.8 to 1.1-2.8 W/m².K), which a curtain cannot match. A high-density multi-layer thermal curtain reduces losses by 20 to 30% and also provides blackout (100%*) and sound attenuation (22 dB*). It is an effective complement, not a replacement.
Is a thermal curtain useful with double glazing?
Yes. Even with good double glazing (Ug 1.1-2.8 W/m².K), the window remains the thermal weak point of the dwelling (resistance 5 to 10 times lower than an insulated wall). The curtain adds an extra layer of insulation (R 0.3-0.6), eliminates any residual cold wall effect, blocks light for sleep, and attenuates outdoor noise by 22 dB*.
How much does double glazing cost compared to a thermal curtain?
For a dwelling with 5 windows: double glazing 3,000 to 10,000 euros (supply and installation), custom thermal curtains 400 to 1,300 euros. A ratio of 1 to 10. Aid (MaPrimeRénov' 40-100 euros/window, CEE 30-80 euros/window) reduces the cost of double glazing, but the curtain remains 5 to 8 times cheaper after aid. For tenants, the curtain is the only viable option because it is transportable.
Does a thermal curtain really reduce heating bills?
Yes. For a 60-80 m² dwelling with 5 windows and electric heating, the estimated saving is 60 to 150 euros per year with high-density thermal curtains (620 g/m²). The effect is more pronounced on single-glazed windows (savings closer to 150 euros/year) than on recent double glazing (savings closer to 60 euros/year). ADEME estimates that windows account for 10 to 15% of a dwelling's heat loss.
What advantages does a thermal curtain offer that double glazing does not?
The multi-layer thermal curtain provides three functions that double glazing alone does not cover: total blackout (100%*), sound attenuation (up to 22 dB*), and sun protection in summer. It is also reversible, transportable in case of moving, and can be installed without any authorization. Double glazing is fixed, permanent, and blocks neither light nor noise.
Is financial aid available for thermal curtains?
No. Public aid (MaPrimeRénov', CEE, interest-free eco-loan) concerns only structural energy renovation work, including window replacement. Thermal curtains are not eligible because they are reversible and non-structural. However, their cost (80-200 euros per window) is already 5 to 10 times lower than double glazing before aid.
Thermal curtain or triple glazing: how to choose?
Triple glazing (Ug 0.5-0.8 W/m².K) offers the best possible thermal performance but costs 50 to 80% more than double glazing, i.e., 600 to 1,500 euros per window including installation. It is relevant in new RE2020 constructions and very cold regions. For existing homes, the combination of double glazing + multi-layer thermal curtain generally offers a better cost/performance ratio than triple glazing alone, with the added benefits of blackout and sound insulation.
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