I also decided to use some cheap closed cell foam that I had around the house from a cheap sleeping mat. This is the kind that they sell for 5-6 dollars at the discount stores in the camping department. I cut out a shape that will end up being the size and shape for the bottom of the outer bootie. This foam pad will be an insulating member inside the bootie.

I think my first attempt at the outer bootie will be a relatively snug fitting and low loft design. Then I may make a higher loft more wind resistant design for even colder temperatures.