What are thermal curtains, and how do they work?

What are thermal curtains?

Also known as insulated curtains, they are made from multi-layer fabrics: a decorative layer, an insulating layer (made from felt, polyester or denser fabrics) and sometimes a reflective polyester or aluminium backing. They are ideal if you’re aiming for a more sustainable home without sacrificing comfort, as they combine functionality and aesthetics.

Essentially, they are standard curtains made with special materials —usually thicker fabrics, insulating linings or intermediate layers, as mentioned above— designed to provide thermal insulation in addition to blocking outside light and ensuring privacy.

Thanks to this composition and blend of materials, when properly fitted to the window frame, thermal curtains create an ‘air pocket’ or insulating barrier that reduces heat loss in winter and blocks heat gain in summer.

Types of thermal curtains

There are several types designed to ensure thermal insulation, with varying levels of effectiveness depending on the material, thickness and type of fabric used. The most common options on the market include:

• Multi-layer thermal curtains: the most popular choice for residential settings. These combine a decorative outer fabric, an insulating middle layer and an optional thermal backing for enhanced efficiency.
• Thermal blackout curtains: ideal for bedrooms or areas where darkness and comfort are key. In addition to minimising indoor heat loss, they block almost all external light.

Although less common in standard homes, thermal curtains with more technical treatments are designed to improve energy efficiency in entire buildings or industrial environments, such as warehouses.

The right choice depends on your needs and your goal. For example, a living room may only require a thick multi-layer thermal curtain, while a bedroom with large windows will benefit more from thermal blackout curtains.

How do thermal curtains work?

Their performance is based on the effect of special materials that reduce heat transfer. This technology not only improves indoor comfort but also helps reduce energy consumption.

The multiple layers serve a specific purpose: trapping air to minimise heat loss. In winter, they retain the heat generated by heating systems, preventing it from escaping through windows. In summer, they block excess heat and sunlight, keeping interiors cooler.

Considering that around 13% of energy from heating and cooling systems is lost through windows, thermal curtains can reduce heating-related electricity costs by 40% to 50% and lower indoor temperatures by 4 to 7 °C during summer.

How much can thermal curtains help you save?

Exact savings depend on several factors —type of home, heating and cooling systems, window quality and usage habits— but various energy experts agree that thermal curtains can significantly contribute to energy savings.

Poorly insulated windows account for nearly 30% of energy loss in a home. Regarding estimated savings, multiple sources indicate that installing thermal curtains can reduce heating demand by 40% to 50% during winter.

While there is no universal savings percentage for every household, thermal curtains are proven to noticeably reduce electricity consumption —especially when combined with other insulation solutions.

Benefits of thermal curtains

Thermal curtains go beyond decoration, offering practical benefits that enhance comfort and energy efficiency thanks to their insulating properties. They also help reduce energy use and can even block outside noise:

Energy and cost savings

• They reduce the need for heating and cooling systems and, therefore, electricity consumption, by minimising heat loss in winter and limiting heat gain in summer.
• These curtains lower electricity and gas bills by promoting significant energy savings —especially important in homes with high climate control costs.
• According to technical estimates, they improve the thermal insulation coefficient (U-value), limiting the rate of heat transfer.
• Since they are relatively affordable and require no construction work, the return on investment is much faster than with other insulation alternatives. 

Thermal and acoustic comfort

• Their dense fabrics and multiple layers help dampen outside noise.
• They eliminate the ‘cold wall’ effect near uninsulated glass. This way, they contribute to a more stable and uniform indoor temperature while preventing sudden fluctuations, which enhances overall comfort.
• They also help reduce cold or hot drafts entering the home.

Style and décor

• Thermal curtains are available in a wide range of designs, textures and styles —from fine velvet to eco-friendly options made with organic cotton and linen.
• They are highly versatile for home décor, combining aesthetics and functionality while fitting seamlessly into living rooms, bedrooms and offices without drastically altering the space’s appearance.  

Limitations of thermal curtains

It’s important to note that thermal curtains are not a perfect solution and do not fully replace proper structural insulation. Their main limitations include:

• Correct installation is essential for effectiveness. If the window is not fully covered or gaps remain, insulation will be incomplete.
• They do not solve structural insulation problems such as air leaks, poorly sealed window frames or thermal bridges in walls, floors or ceilings. In these cases, thermal curtains act only as a complement.
• Window replacement and insulation of walls, floors or ceilings will always be more effective. Compared to these major upgrades, thermal curtains are less expensive but also offer more limited performance.

Thermal curtains versus other insulation solutions

To properly assess their effectiveness, it’s useful to compare thermal curtains with other insulation options commonly used in homes:

Thermal curtains versus double glazing

Double glazing requires renovations such as replacing windows and improving frames and seals. It provides permanent insulation and significantly reduces heat loss or gain —much of which occurs through windows, doors, joints and seals.

On the other hand, thermal curtains complement these structural solutions. They add extra insulation but do not correct thermal bridges or defective windows. While very useful, they do not reach the same efficiency level as well-insulated windows. However, their low cost and easy installation make them an attractive intermediate solution.

Thermal curtains versus draught excluders

Draught excluders (for joints, frames, windows and doors) are another simple way to prevent draughts by sealing gaps where air leaks occur. While it does not fully replace proper window or wall insulation, combining draught excluders with thermal curtains improves overall insulation performance.

Thermal curtains versus roller blinds

Roller blinds are typically lighter and function differently. They are mainly designed to control light, provide privacy and enhance aesthetics rather than to provide thermal insulation. Although some blinds have insulating properties, they generally retain less heat or cold than thermal curtains due to fewer layers, less insulating material and lower fabric density. If your goal is energy efficiency, thermal curtains are usually a better option than standard roller blinds.

Overall, thermal curtains strike a perfect balance. They offer better performance than lightweight curtains or blinds while remaining far more cost-effective than structural renovations. Furthermore, they are fully compatible with draught excluders and other sealing improvements.

Where and how to install thermal curtains

To ensure optimal performance and maximum insulation, keep these recommendations in mind when installing thermal curtains:

• Hang them as close as possible to the window frame. Ideally, place them touching the wall or moulding to minimise gaps where air or heat can pass through and to maximise their insulating effect.
• Make sure they cover the entire glass surface, extend to the floor or windowsill and overlap in the centre if they are split into two panels. This helps reduce draughts.
• If possible, install a valance or pelmet at the top to limit air circulation (hot or cold) behind the curtain.
• Use them strategically: keep them closed at night in winter to retain heat; close them during peak sunlight hours in summer to reduce heat gain. This way, you’ll maintain a comfortable indoor temperature.
• Install insulated curtains in high-priority areas such as rooms with single-pane glass, windows facing south, east or west, and balconies or large glass doors.
• Perform regular maintenance. Vacuum them regularly to preserve their insulating properties.

Are thermal curtains worth it?

The answer depends on several factors and scenarios: the type of home and windows, local climate, usage habits and the level of comfort desired.

In homes with inefficient windows or limited insulation in regions where winters are mild, thermal curtains can be an effective, simple solution with a quick return on investment.

They are also a smart choice for homes with old or poorly sealed windows where replacement is not planned due to cost, where reducing heating or cooling bills is a priority and where improved comfort is desired without construction work.

If your home already has efficient double-glazed windows and good overall insulation, thermal curtains become less essential. In that case, they mainly serve as a decorative complement that slightly enhances comfort without dramatically changing energy consumption.

Thermal curtains combine climate control, savings, style and sustainability in a single solution. They are a smart, accessible and effective way to improve a home’s energy efficiency without renovations. Thanks to their technical materials, they help reduce heat loss in winter and heat gain in summer.

And when combined with an Endesa electricity plan tailored to your needs, you can get even more value from this versatile and functional accessory —reducing electricity consumption during peak usage periods and lowering your monthly energy bill.