Stop in for a cup of coffee

Whats everyone using for sound deadener/insulation that doesnt cost an arm and a leg. I've seen something about what you can buy at the local home store, but looking for options. I need to get something in my car so my feet dont get so damn hot.
If you’re only after heat reduction, I’ve always wondered what Mylar would do. It’s light, durable in layers and they used it to fly in space and land on the moon in conditions where it was 200 degrees in the sun and -200 in the shade.