After 1-1/2 years I can report on the success of exterior window film for reflecting much of the suns energy before it passes into the window. The problem with interior reflective film is that the sun energy passes through the glass twice. This heats up the glass and much of this heat is transmitted into your home. Heavy curtains will stop the sunlight after it passes into your home. They will heat up and most of this heat will transfer into the rest of your home.
The exterior film reflects much of the sunlight before it enters the glass.
The product I purchased and installed is:
BDF EXS15 Exterior Window Film Privacy and Sun Control Silver 15, Dark - 24in X 50ft
This is for people who have already purchased and installed windows for their home and did not get the low-e coating and renters who want a quick low cost solution to a window they do not own.
Maybe you can figure out a way to buy the same quality from China and save costs. I purchased from the US to improve the chances that I was getting a quality product for exterior use. If it was interior I would not be worried about the quality.
There are a number of YouTube videos that show the tricks on how to install window film.
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