What you need:
insulation board or foam board (which is way cheaper and you can glue layers together to make it as thick as you like)
hot glue gun
pencil or pen
no-damage velcro picture hanging tabs
First thing I did was measure my windows and cut my insulation board to the proper size which was just a tad bit bigger than the length of the window. Then I cut my fabric to a size that was bigger than my board pieces so that it could be wrapped around the board.
I lay the board down flat on top of the fabric. Then I wrapped each side over the board. Before I glued the edges down I cut a piece out of the fabric at each end on one side. This is where I would later stick the hanging tabs on. I then glued the edges down.
After gluing the edges down I folded the ends over and glued those down too. Mine is a little messy but no one will see the back.
It looked like this when I was done gluing:
Now I was ready to put the hanging tabs on. I used these:
I put one on each end of each of my boards where I had cut out the material and left a space. Before I put them on I glued on some pieces of foam board to make a small space between my valance and the wall when they are hung up.
Then the hard part! Hanging them up straight and even! I just measured it out and made tiny marks on the wall so I would know where to place each board.