In most retail listings "thermal curtains" and "thermal insulated curtains" are used interchangeably, although they technically are different things. Buying the right thermal curtain requires an understanding of the construction of the curtain, so you do not waste your money on cheap, stiff, ugly curtains.
The construction type determines the value of the curtain, though it's often hardest to determine given the construction type.
Walk through the aisles of your favorite big box store, and you'll see "thermal curtains" and "thermal insulated curtains" used as if they mean the same thing. In most circumstances, they do. They both are curtains that are built to minimize the transfer of heat through the integrations of your windows.
Unfortunately, there are many differences in the construction of thermal curtains. A $25 cheap foam curtain and $150 high-quality interlined drape might both say thermal, but can actually be built of entirely different materials and construction. This also applies to the use of the term. A curtain that is built well, looks good, and works well will often be marketed the same as the stiff, plastic panel that you will regret buying.
Three kinds of construction of thermal curtains
Since thermal curtains can be built in a lot of different ways, understanding those ways will help you make an informed choice.
| Construction type | Mechanism | Advantages | Disadvantages |
| Foam-backed coating | Acrylic foam sprayed directly onto fabric (1-pass or 3-pass) | Affordable, good insulation, strong blackout | Stiff, crinkly texture, can look cheap, not machine washable |
| Triple weave | Three fabric layers woven together with a dark middle yarn | Soft drape, machine washable, no coating to crack or peel | Less insulation than foam-backed, blocks 80-95% of light (not 100%) |
| Interlined | Separate flannel or bump cloth layer sewn between face fabric and lining | Best insulation, luxurious drape, looks high-end | Most expensive, requires dry cleaning, heavier weight |
Most inexpensive thermal curtains will have foam-backed coating. While the foam does great in blocking heat and light, a lot of people find the fabric to be stiff, likening it to a shower curtain. The coating can crack or peel over time and will definitely do so if it is put in a machine wash.
The popularity of triple weave construction has grown because it solves the problem of stiffness, which is achieved by not coating the fabric and instead weaving three layers together. The fabric will be softer and will have a better drape. The trade-off is achieving slightly less thermal performance and not achieving full blackout.
If the budget allows it, interlined curtains are the better option. A cotton flannel bump, also known as a domette, is sewn between your decorative fabric and the lining. This construction technique, which is only found at custom workrooms or higher-end retailers, creates air pockets that are excellent for insulation while also providing a luxurious drape.
100% Blackout
Better sleep
Noise Reducing
Energy SavingWhat to really look for when you are buying curtains
Curtain companies have a lot of marketing jargon, so look for the specifications of the product instead. Here are the most important ones.
Fabric weight is important, as curtains that are heavier typically offer better insulation. This is measured in GSM, which stands for grams per square meter. Curtains that are made for thermal insulation typically weigh between 200 and 400 GSM. Curtains below 200 GSM will offer little to no temperature regulation. However, most US retailers don't list GSM. If you can't find it, check the shipping weight instead. A single 84-inch thermal panel should weigh at least 2-3 lbs. If it weighs 1 lb, it's a sheet, not a shield.
The details of the construction are important. Descriptions that include "foam-backed," "acrylic coating," or "3-pass blackout" indicate a coated construction. "Triple weave" or "woven blackout" offer the softer alternative. "Interlined," "bump cloth," and "flannel interlining" indicate the higher quality construction.
Before purchasing, read reviews analyzing texture. Specific reviews mentioning words like "stiff," "crinkly," or "plastic" may indicate substandard products covered in foam. Note multiple reviewers mentioning these issues in their reviews.
Double-check washing instructions. Curtains with foam backing typically require dry cleaning or spot cleaning only. Other constructions, like triple weave, are often machine washable. This is important if you have pets, kids, or allergies.
The stiffness problem (and how to solve it)
Thermal curtains have a foam coating that makes them functionally effective. This coating is also what makes them hang stiff. Foam coating curtains stiffen movement, thus, they can never mimic the soft, flowing drapes you see in design magazines.
If you want the efficient thermal performance without the plastic-curtain aesthetic, you may:
Buy triple weave curtains and accept slightly less insulation for a fabric that actually drapes well. For most climates, the difference in thermal performance is minimal.
Use a separate thermal liner behind decorative curtains you already love.
Set realistic expectations
Curtains that retain heat help insulate your home, but they don't work miracles, and they won't save you money.
Windows are a huge part of heat loss in a home. One of the biggest culprits is single-pane windows, which only have a thermal resistance (R-value) of about R-1. R-values are a measurement of insulation that windows possess. Double-pane insulated windows perform a little better, roughly R-2 to R-3, which is still terrible. As a frame of reference, R-values in insulated walls are usually R-13 to R-15.
When closed, a standard hanging thermal curtain typically adds about R-1 to R-2. You can reach up to R-3 only with a sealed installation that includes a pelmet (a box valance at the top) and side returns to block airflow at the edges. That helps mitigate heat loss by about 25-40%. But this only works if you actually close the curtains, and it still won't address the fact that the rest of your home is losing heat.
Another thing to keep in mind is that thermal curtains only work when they're closed. If you keep them open to let light in during the day, you don't get the thermal benefits. During the winter, some homeowners open south-facing curtains to gain solar heat and then close them when the sun goes down to keep the heat in.
Match your climate
In some situations, technologies that retain heat are better than others.
Cold climates: Curtain insulation should keep heat in. Heavier curtains offer better sealing against airflow. Curtains that are longer and puddle on the floor create an even better seal. Curtains that are fitted to cover the wall edges rather than just the window reduce airflow circulation. For maximum insulation without adhesives, use wraparound curtain rods (also called French return rods). These curve back into the wall at each end, eliminating the side gap between the curtain and the wall.
Hot climates: Curtain insulation should keep heat out. For summer heat blocking, the backing (the side facing the window) must be white or light-colored to reflect sunlight and solar radiation. The front color of your curtain can be any shade you like for decor purposes, but if that front fabric is dark and there's no reflective backing, it will absorb heat and radiate it into the room. This is why foam-backed curtains (3-pass) often perform better in summer, since the back is almost always white regardless of the front color. Triple weave curtains without a white lining can actually make rooms warmer in direct sun.
Mixed climates: Triple weave curtains with a white or light-colored backing are versatile year-round. They offer insulation for the winter and heat blockage for the summer. They don't come with the downsides of heavily coated fabric.
FAQ
Are thermal curtains the same as blackout curtains?
Not exactly, although there is some overlap. Thermal curtains aid in energy efficiency by helping to keep the temperature in a room at a comfortable level. Blackout curtains aid in light control. However, some curtains have both features. Thick curtains may keep the temperature regulated while also blocking light. Check the product description to confirm. Most curtains marketed as "thermal" will only block 70-80% of the light unless they specify "blackout."
Do thermal curtains work in summer?
Yes. The same insulating properties that keep heat inside during the winter also keep heat outside during summer. If closed on sunny windows, thermal curtains can reduce solar heat gain by 25-33%. Light-colored curtains with white or reflective backings work best for summer heat blocking. If your curtains have a dark front and no white backing, they may actually absorb heat and warm the room.
Why do my thermal curtains feel stiff and plastic-like?
It's possible that you have foam-backed curtains. The insulating foam covering the back of the curtain stiffens the fabric. If you prefer a softer look, you might want to look for curtains with triple weave construction or consider using a separate thermal liner behind decorative curtains.
What are the best practices for hanging thermal curtains?
For best results, hang them as close as you can to the window frame. To reduce air circulation, extend the curtains at least 3-4 inches beyond the window on each side. Curtains that are floor-length and touch the floor or have a little extra length (puddle) are better than shorter curtains. For a polished look without adhesives, use wraparound curtain rods (French return rods), which curve back to the wall and eliminate side gaps.
Can thermal curtains be washed in the washing machine?
It depends on the type of thermal curtains you have. In general, foam-backed curtains cannot be washed in a machine, because the foam can crack or peel. Triple weave curtains can often be washed in the machine on gentle cycles, but always check the care label. Professional cleaning is usually the best option when it comes to interlined curtains that are expensive.
