Why Your Blackout Curtains Still Let Light In (And How to Fix It)

Many people think buying blackout curtains is simple.

Choose a dark color, hang them up, and enjoy a perfectly dark room.

Unfortunately, that's not how blackout curtains actually work.

If you've ever bought curtains labeled "100% blackout" only to wake up with sunlight shining through the edges, you're not alone. In reality, achieving a truly dark room depends on much more than just the curtain fabric.

After hearing the experiences of many homeowners—and helping customers choose the right curtains—we've found that these are the biggest mistakes people make.

1. The Curtain Is Only Half the Story

One of the biggest surprises for first-time buyers is that installation matters just as much as the curtain itself.

Even high-quality blackout fabric won't perform well if light leaks around the edges.

For maximum blackout performance:

Install the curtain rod 10–15 inches (25–38 cm) above the window frame.
Extend the rod 8–10 inches (20–25 cm) beyond each side of the window.
If possible, use a wraparound curtain rod so the fabric touches the wall instead of leaving gaps.

This simple change dramatically reduces light entering from the top and sides.

Many people blame the curtain when the real problem is the installation.

2. "Room Darkening" Is Not the Same as "Blackout"

These terms are often confused.

Room Darkening Curtains

Reduce brightness
Create a softer atmosphere
Still allow noticeable daylight to enter

Blackout Curtains

Block nearly all incoming light
Ideal for shift workers, nurseries, media rooms, and bedrooms
Usually require either a blackout liner or a dedicated blackout backing

If complete darkness is your goal, always check how the curtain achieves its blackout effect—not just what the product title says.

3. Blackout Coatings Can Sometimes Produce Odors

Some inexpensive blackout curtains rely on a chemical coating applied to the back of the fabric.

While effective at blocking light, these coatings may produce a noticeable smell when new, especially in enclosed bedrooms.

If you're sensitive to odors, a better solution is to choose curtains with a sewn-in blackout liner instead of relying solely on coated fabric.

A quality liner provides excellent light blocking while avoiding the strong plastic-like smell that some coated curtains can have.

4. Fabric Thickness Matters More Than Color

Many shoppers assume darker colors automatically block more light.

That's not always true.

A thick, well-constructed curtain often performs much better than a thin dark-colored fabric.

For example, chenille curtains are naturally:

thicker
softer
better at absorbing sound
better at reducing heat transfer

If additional darkness is needed, adding a blackout liner creates an excellent combination of comfort and performance.

5. Blackout Curtains Can Also Make Your Room Quieter

Although curtains won't completely soundproof a room, heavier fabrics can noticeably reduce everyday noise.

Many homeowners find that thick curtains help soften sounds like:

traffic
tire noise
neighborhood activity
echoes inside the room

The heavier the fabric, the greater the sound absorption tends to be.

6. They Can Help Keep Rooms Cooler

Windows allow a significant amount of solar heat into a room.

A thick curtain acts as an additional insulation layer, helping reduce heat gain during the day and slowing heat loss during winter.

Many customers notice that rooms with heavier curtains stay more comfortable and may require less air conditioning during hot afternoons.

7. Curtain Width Is One of the Most Overlooked Factors

This is one of the biggest mistakes homeowners make.

Buying curtains that are approximately the same width as the window creates gaps in the middle and along the sides, allowing sunlight to leak through.

For proper fullness and better blackout performance:

Total curtain width should be 2–3 times the width of the window.

For example:

Window width: 60 inches
Total curtain width: 120–180 inches

The extra fabric allows the curtains to overlap naturally, minimizing gaps and creating a fuller, more luxurious appearance.

8. The Best Blackout Setup Is a Complete System

Many people spend hours comparing fabrics while overlooking the other factors that matter just as much.

The best blackout performance comes from combining:

thick curtain fabric
a quality blackout liner
proper curtain width
correctly installed curtain rods
wraparound hardware
enough fabric to fully cover the window

When these elements work together, the difference is dramatic.

Final Thoughts

Finding effective blackout curtains isn't just about choosing the most expensive product or the darkest color.

The best results come from understanding how the entire window treatment system works together.

A properly sized curtain, installed high and wide, made from thick fabric, and paired with a quality blackout liner will outperform many products that simply advertise "100% 

blackout."

If you're investing in new curtains, don't focus only on the fabric. Pay attention to installation, sizing, lining, and fabric construction—the details that truly make the difference between a room that's merely dim and one that's genuinely dark.