I wanted to keep the shade light in colour so that it wouldn't absorb heat from the sun. I had some white embroidered cotton fabric left over from a shirt I previously made but thought it was a bit too thin, plus the tiny holes in the design could let streams of sun in and annoy a sleeping baby. Since the fabric was so pretty I used it anyway but added a second layer of cotton on the underside.
Next I added an elastic to one end of the shade so that it could easily hang around the back headrest. Between the two points where the elastic attaches to the fabric I attached a wooden stick to keep the cloth from drooping in the middle.
On the other side of the shade I attached a thicker and stronger elastic encased in the last scraps remaining from Adam's citrus nursery curtains and chenille blanket. I wanted this elastic sling to be more durable since it is going to be pulled on and off the car seat repeatedly. It ended up fitting really well around the top of the baby car seat and keeps the shade nice and taut. When not in use this thicker sling can easily be hung over the back seat headrest as well, folding the shade in half and keeping it nicely out of the way.
Here's the final result. As you can see it did a good job of keeping the sun away from Adam so that he could catch some zzzZZZ's!