The valence is lifted to reveal the homemade mechanism for rolling the curtain.  Materials include Reflectix insulation, wooden dowl, closet flange for the rope spool, rope, tensioner and, the handyman’s special - duct tape.
The rollable insulation is available at most home supply stores.  It is basically bubble wrap with foil facing.  

Compared to a well insulated wall, even the best windows act as thermal holes, transferring a great deal of heat outdoors.  These curtains will triple the R-value of most window areas and are considered invaluable over large patio doors.  A person sitting near an uninsulated window is transferring their radiant energy outdoors through what is basically a window “heat magnet”.  These curtains serve as infra-red barriers, reflecting your body heat back into the room.  Additionally, they mitigate infiltration based on how tight you make them.