Curtains to Keep a House Cool: Block Heat, Let Light in


Most traditional window decorations don’t provide sufficient room darkening and won’t protect your house from the inflow of hot air. With the scorching outdoor temperatures, regular curtains and thin drapes won’t work.

The simplest solution to keep a house cool is to hang thermal curtains that provide only a partial room darkening. The sunlight will be reflected and won’t reach your room that much. This way, the curtains will block heat but let enough light in. 

Let’s have a look at different types of curtains, according to their specific functions and properties.





It’s important to remember that on hot days ordinary curtains transform the house, especially a small one, into a stuffy greenhouse. Thermal curtains would be a great option here as they are a practical way to improve thermal insulation.

The main advantage of thermal curtains is their effectiveness during both winter and summer. Thermal fabrics trap the cold indoors depending on the season and your needs.

In hot weather, thermal curtains reflect the sun rays back to the outside and protect against heat. They are made with a special technology that allows them to reflect 80 to 90 percent of the heat so that you can enjoy a pleasant, cool home on hot summer days. Thanks to these curtains, the room temperature will drop by up to 44.6°F (7°C).


Fabrics with thermal insulation properties

In summer, curtains made of fabrics with thermal insulation properties may be an ideal solution. They are used for protecting rooms from an excessive amount of sunlight from outside, i.e. they don’t let the heat indoors. The use of these curtains provides not only better insulation but also greater privacy due to their thicker material.

People often confuse thermal insulation fabrics and fabrics with thermal insulation properties.

To make it clear, fabrics with thermal insulation properties don’t belong to technical fabrics. They only show certain properties of thermal insulators. And this is a reason why they are also used in the production of window systems. They are being used to sew curtains (and blinds) that prevent overheating of interiors.

In the case of fabrics with thermal insulation properties, we need to emphasize their characteristics such as:

transmission of light (the degree of blackout)

reflection (the degree to which the fabric reflects sunlight)

absorption (the extent to which the fabric absorbs sunlight)

When talking about thermal insulation fabrics, we usually don’t refer to materials for curtains or blinds but specialized fabrics for technical applications.


Windows orientation

The intensity of natural light in rooms depends on the size and orientation of windows, which also affects energy efficiency. North-facing windows receive the least solar gain while south-facing windows receive the most.

The light coming in from the south side is very powerful. Unfortunately, an ordinary curtain doesn’t protect the room against overheating. Despite breaking the directly falling rays, the temperature inside continues to rise. But when thermal curtains are used and properly installed, an air conditioner can run on a lower setting, which saves energy.





A popular variant of thermal curtains is the blackout type, characterized by a very high degree of blocking out sunlight. This is a perfect solution for people who get their sleep disturbed by the morning sun. Reflection (the extent to which a given fabric reflects light), and absorption of sun rays, both play a significant factor in this matter.

If you prefer a total blackout, the most effective will be curtains made of a special dim-out material (blackout fabric). They will darken your room at a minimum of 90 percent. This is possible due to the dense thread weave responsible for light transmission.

It’s also worth paying attention to the unique thermal insulation properties of blackout curtains. They protect the room against cold in winter, contributing to savings on your heating bills. In turn, in the summer, they will act as an effective barrier against the sun and heat, in a way an air conditioner does.

Even though thermal curtains can be designed to block light, not all thermal curtains are blackout curtains. Many of them darken the room only due to the thick materials used. If the middle layer in the thermal curtains is made of black felt or a real blackout material, the drapes will have both blackout and thermal properties.

The tightly woven fabric that blackout curtains are made of, prevents light from getting through the material. Their thin linings or interiors are usually not as effective at blocking heat exchange as thermal curtains. Even though these materials block light and a source of heat, they don’t provide the same level of insulation as thermal curtains.

However, some blackout curtains are made of insulating materials, so they can also be used as thermal curtains. By having blackout curtains with thermal insulation properties installed over a window, we can limit the heat in the house.


Choose a suitable degree of blackout

The specific structure and carefully selected thickness of a blackout fabric will guarantee either partial or complete darkening of the interior. That means you can decide how much light you want to let in.

When choosing curtains, you must pay special attention to the quality and specifics of the fabric from which they are made. The degree of darkening can be very different and it may turn out that the product will not meet your expectations.

The best blackout curtains are made only from the highest quality blackout fabrics, with a darkness level of a minimum of 90 percent. Thanks to this, it’s possible to achieve the most desirable effect of nearly complete room darkening. You will also fully appreciate the advantages of thermal insulation.


In which rooms do blackout curtains work best?

When we talk about blackout curtains, the bedroom immediately comes to mind. After all, it’s mainly where we sleep and relax, so we should darken the room the most. Considering only the blackout properties of curtains, you should first decide to hang them in the bedroom.

For the same reason, it’s also useful to hang blackout curtains in a children’s room, especially if the child still requires afternoon naps.

However, when we look closely at the specifics of blackout fabrics and their thermal insulation properties, we certainly will value using them also in the living room, especially on hot days.





When choosing curtains, we often think about their texture, color, fabric, length, patterns, and whether they will blend in well with the rest of our interiors. Without any doubt, this influences the choice we make. But it’s also worth paying attention to the darkening function which is the most important function that curtains should perform.

Curtains can darken a given room to various degrees. If we choose the right material, they can let light in, hiding the room’s interior from the eyes of passers-by. They can also darken it completely, not letting any light in and thus not causing it to heat up in summer or lose heat on cold days. By blocking the unwanted beams and glare, room darkening curtains will keep the indoor temperature at an ideal level.

If you want to let light in but block heat, it’s worth paying attention to curtains light absorption. The higher its value, the less light will enter from outside. Room darkening curtains are somewhat transparent so they effectively reduce the amount of sunlight and better protect interiors from overheating.

Stylish window darkening curtains are popular because of their light-blocking feature. But they still pass some degree of light to enter a room, thus, you don’t need to worry that you turn your room into a cave.

So if you are looking for something that doesn’t block the light completely but obstructs the view from the outside, then room darkening curtains are your best bet. Also, they can last for a long time.

Just like blackout curtains, one of their features is that they can reduce the energy costs of your home. At the same time, they reduce the sunlight that damages your wood furniture and flooring.




Even lightweight drapes made with linings can be used to effectively reflect solar radiation so that you can keep the heat out while still allowing light in.

U.S. Department of Energy claims that, during the summer, as much as 33 percent of heat gain can be reduced by simple light to medium-colored drapes with a white, plastic, thermally reflective backing.

Adding thermally reflective backing to the lined drape fabric creates some important advantages over an unlined drape.

The lined drapes protect against the cold in winter and they stay cooler than some other window treatments in summer. This is due to the fact that their pleats and folds lose heat through convection, and thus, providing you with an energy-efficient and aesthetically pleasing window treatment.

Lined drapes can last 10 to 15 years longer than unlined ones because the lining protects the face material from sun damage. Curtains with lining significantly reduce the amount of light pouring into the room. If you want to darken your room, for example for sleeping, just add a blackout lining to the drapes.


What material is good for curtains?

When choosing curtain fabrics, you should pay attention to the technical specifications. A properly selected material will make it possible to regulate the amount of light coming in from outside.

As previously mentioned, apart from the light transmission, each of the fabric is characterized by different parameters, i.e. light absorption and reflection.

Fabrics that let light through (transmit light), only partially limit the penetration of sunlight.

Properly selected curtains guarantee long and useful functioning. When choosing, pay attention to the material and quality of the product.


∻ Density

Since the primary function of curtains is to darken the room, it can rightly be assumed that the basic selection criterion will be the fabric weight, in other words, its density. This is correct although you can find curtains fabrics that are highly darkening but relatively light. You can also create a two-layer curtain with thinner, lighter materials, by sewing in an extra lining between layers.


∻ Color

Among semi-permeable fabrics, light materials will let in more natural light than dark ones. Dark materials will make the whole room darker. This is due to their absorption of solar energy.

White and thick curtains are great ways for dealing with summer heat at home. Curtains made from light materials don’t heat up as quickly as dark ones, they reflect a significant amount of the sun rays, blocking more heat.


∻ Fabric

The most popular fabrics used in window systems include polyester and cotton. Some manufacturers supplement these fabrics with additional layers, which increase the properties of the room darkening, sunlight reflection, or absorption.

A large group of fabrics that are used in the production of curtains is plush material, such as velvet, but also silk, linen, or even wool.


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Protect home furnishings with curtains

Protecting the interiors from excessive heat and sun exposure is also very important for the furniture and wooden floors.

Under the influence of sunlight, wooden surfaces, leather furniture, or fabric upholstery become discolored to varying degrees. Depending on the time and intensity of sunlight, areas exposed to direct sun rays are cracked and damaged more quickly.

Drawing or putting up the curtains provides shade and protects your home furnishings.


In Conclusion,

When you replace your ordinary fabric curtains with the ones that block heat but allow some light in, you will definitely feel the difference. And that’s not only in the temperature in your house but also in your electricity bills as you will need to run your air conditioning much less.