Blackout curtains can keep out the heat from the sun better than normal curtains.
But how about using roller shades with blackout fabric instead?
These DIY roller shades with blackout fabric fromThrift Divingon Youtube are not only cheap but also effective.

Image credits: Thrift Diving via Youtube
Watch the video tutorial below to learn how to make them.
confirm your fabric has the right angle youre working from that is square.
The measurements of this depend on how big your windows are.

But before pressing it, place the blackout fabric so the seams will be folded onto the blackout fabric.
Use adhesive spray to secure both fabrics together.
(Use pins on top to align it.)

After pressing, sew the edges.
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Step 2
Next, remove the vinyl from the roller shades.
Put double-sided tape, then attach the black-out fabric to the rod.
Roll it slowly and verify that its going to the rod straight.
After this, mount the brackets to the inside of your window.
Place the rod with the blackout fabric, then reset the tension by pulling it and then releasing it.