Posted on: 18.12.2022 Posted by: Редакция Comments: 0

We all know that curtains can help cool a room by blocking direct sunlight, but we often don’t think about the fact that curtains can also have the opposite effect in colder months.

In fact, curtains can make a room warmer. The color, thickness, material, placement of the curtain relative to the window, and other factors unrelated to the curtains can affect the temperature of a room.

But how exactly do curtains make a room warmer? In the following sections, I will explain how curtains can heat your house (or not). Since thermal curtains are best suited for keeping a room warm (spoiler alert!), I will briefly discuss them and show you how to choose the best curtain for yourself.

How do curtains affect the temperature of a house?

When we talk about how curtains affect room temperature, it is assumed that the curtains are closed. Otherwise, the effect is less pronounced.

Curtains can change the room temperature by regulating the heat that comes through your windows and trapping the heat already present in the room.

Curtains affect the temperature of a house by reducing the amount of sunlight that enters a room. If there is already heat stored in a room, curtains can prevent some of that heat from escaping through the windows.

The choice of the right curtain material, color, and placement is crucial.

All curtains can block sunlight, although they each have different degrees of ability to do so. Their ability to do so depends on:

  • Color: A darker curtain absorbs more light (which is subsequently converted into heat) than a lighter one. The darker the curtain, the warmer the room.
  • Material: For example, blackout curtains can block up to 99 percent of sunlight due to their double-layered and tightly woven fabric.
  • Placement: Where you place your curtains determines how effectively they will keep your room warm or cool. If you install thick, dark curtains in an already hot room, the room will stay warm, which is not ideal if you are trying to cool the room down. But if you are trying to heat a room, thick, dark curtains will help prevent the escape of room heat.

Curtains can prevent some of the heat from entering or leaving a room.

Imagine if there were a gap between the window and the curtain. In this case, cold air could enter the room through convection, where heat rises (i.e., out the window) and cold flows down (i.e., through the gap under the curtain and into the room).

Assuming there is no gap between the curtain and the window, if the outside temperature is lower than the inside temperature and the room is already warm, the curtain can block cold drafts.

As you can see, even blackout curtains cannot block all sunlight from entering a room. They can reflect most of the sunlight outside, but some heat remains in the room.

Heavy, thick curtains with insulating properties can warm a room.

The best curtains for retaining heat are heavy, thick, and have solid insulating properties. To understand how insulated curtains work, you need to know what conduction and insulation are.

Conduction involves the transfer of heat energy between neighboring molecules, causing those molecules to vibrate faster (i.e., heat up). If a room has no curtain and the outside temperature is colder than the inside temperature, heat will move into the colder room.

If you want to prevent heat losses in a room due to conduction, you need to install a material over a window that does not conduct heat well (i.e., a thermal insulator). Insulated curtains trap air in the room, which means that the hot air has less opportunity to come into contact with the cold air from the window and flow there.

Keep in mind that conduction involves the rapid vibration of molecules. The denser an object is, the more likely it is to become hot through conduction. Since gases (such as air) have molecules that are further apart than solids, heat is transferred at a slower rate.

We have addressed what types of curtains are best suited for heat retention. Let’s dive into the ones below.

What kind of curtains can trap heat inside?

As I mentioned earlier, some curtains keep a room warmer than others. If you want a curtain that keeps the heat inside (instead of blocking heat from the outside), there is only one choice.

Thermal curtains can trap heat inside. They primarily act as insulators but can also have other properties. Thermal curtains differ from blackout or solar curtains, which prevent sunlight from entering a room.

How to choose the best thermal curtains

Before looking for the best thermal curtains available online, you need to know what to look for. Below are some tips for choosing the thermal curtain that best suits you.

Here’s how you can choose the best thermal curtains:

  • Choose the right size and length for your window.
  • Check the R-value.
  • Consider purchasing additional features.

Let me explain these tips in more detail.

Choose the right size and length for your window

Take a tape measure and find out the length and width of your window. Then measure the distance from the highest point of the window to the floor. A good curtain should reach the floor and be at least twice as wide as the window.

Check the R-value

Any thermal curtain worth its salt should come with a specification regarding its R-value. The R-value measures the effectiveness of a curtain as an insulator. In other words, the higher the R-value, the better its insulation capabilities.

Consider additional features

While insulation is the main function of a thermal curtain, it is not the only feature you should consider.

For example, some thermal curtains also serve as blackout curtains, which store heat and block sunlight. You can also find thermal curtains with triple-layered fabric and soundproofing materials.


Curtains can make a room warmer, provided the right variables are in place. The curtains must have strong insulating properties, a dark color, and a fit that prevents heat from escaping through convection and conduction.


  • Quora: Do blackout curtains make a room warm?
  • Quora: How do black curtains affect room temperature?
  • Reddit: Do dark window curtains keep a room cool? Or does heat hit the curtain and distribute into the room?
  • Home Decor Bliss: Do Curtains Block UV Rays?
  • HVAC Seer: Do curtains provide insulation?
  • ZebraBlinds: Do blackout curtains block heat?
  • Choose: 7 Best Blackout Curtains To Consider, According to Experts
  • Merriam-Webster Dictionary: Definition of Convection & Meaning
  • UCAR Center for Science Education: Conduction
  • Scientific American: Stay Warm with Thermal Insulation
  • Royal Society of Chemistry: Insulation and Conduction: Thermal and Electric Insulation and Heat Conduction
  • CK-12 Foundation: Thermal Conductors and Insulators
  • Family Handyman: What to Know About Thermal Curtains
  • Bustle: The 3 Best Thermal Curtains To Keep Heat Out
  • Simply Blinds: Guide to Curtains and Window Treatments
  • Insulation

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