uses a layer of foil bubble wrap (Reflectix is commonly sold
at hardware and big box stores) with carpet-like marine headliner on top (available online or through a marine supply store In a range of neutral colors).
Both are fairly easy to work with and can be applied using an automotive headliner adhesive.
Actual insulating value isn’t much, but it works well in practice for 3-season use. Does not absorb water or odors, does not form condensation, and feels soft and warm when you brush against it.