We all know that blackout curtains were designed to block out the light. But they are also advertised to help save you money by keeping the cold out during winter and keeping the heat out during summer. The argument is that blackout curtains are so densely woven that air whether hot or cold is unable to penetrate through the fabric. This might be true but air can nevertheless flow to the left and right of any blackout curtain. A solution to this problem would be to make sure the length and width of the blackout curtain fabric extends much longer than the dimensions of the window. This will help constrain the airflow to a specific area. It would also hinder the flow of the air. The closer blackout curtains are to the window glass the better they will be at keeping air out of your house. So technically yes they can help lower your monthly heating and cooling bills.
The same could be said for thick curtains because they too can technically keep a lot of air from passing through your windows. However considering that the fabric of a blackout curtain is so tightly interlaced one would have to agree that they are better insulators than the thickest curtains. So from this standpoint the answer is yes they can help save you money. You would however have to purchase probably twice the fabric length to accomplish this. This can easily double your costs. This is why it is important to think about why you want to buy blackout curtains. If you want better insulation for you home then you must think about other methods. If however you want to a blackout curtain to keep light out then the added insulation benefit is definitely a plus. This is where you need to think carefully before you make a purchase. Some blackout curtains are better designed to blackout and to insulate. These type of curtains are thermal insulating blackout curtains. The blend of fabric they use were specifically designed to block out light and to insulate. They also have thermal lining which further assures that sun nor air are able to pass through the seams.
Blackout curtains are ideal for those who need to block out light for one reason or another. But purchasing blackout curtains solely to insulate your home isn’t the wisest nor the best option. Think about your needs and base your decisions based on those needs. Blackout curtains were manufactured primarily to prevent sunlight from penetrating through curtain fabric. They weren’t primarily designed to insulate.