Reflectix has very little insulating value when used in a sandwich. It is intended to be used as a radiant barrier. It is used by several manufacturers because it is relatively inexpensive and easy to work with. For a bit better performance, you can use un-faced closed cell foam instead of Reflectix with the marine headliner over it. I like the soft-touch surface of the headliner, and the nap creates a little insulating value of its own.
Realistically, since we're typically only talking about 1/4" of material, the added value of foam over Reflectix probably isn't worth the added cost and installation difficulty for most people. Reflectix plus headliner works well enough in practice as long as you don't camp in extremes of heat and cold.
You can also still buy vinyl-faced closed cell foam- a modern version of Ensolite- if you prefer a wipeable surface. I just haven't been able to find a source that isn't black. There must be one out there somewhere, because Escape
uses an off-white version in its trailers. Someone was selling a large roll recently in the classifieds. Don't know if it's still available.