I contacted the manufacturer of my windows; they told me that my windows were manufactured in 2009, do not have Low-E, and do not have argon gas. That being said, they are vinyl double pane single hung windows. The windows have no seal failures and all of them are fully operational.

However, I live in the south, and in the summer months, the windows get too hot to touch, and they allow a lot of heat energy into the home, making the rooms uncomfortable to be in. This is even the case with white blackout curtains covering them all day. The windows get direct afternoon sun for ~6 hours per day.

Therefore, I would like to get window films installed that block as much of the heat energy as possible, but I'm picky, and I want the window films that will prevent energy/heat gain into the window structure to begin with. This means installation on the exterior, not the interior.

But I'm making phone calls to get quotes, and everyone in my area is installing them only on the inside. When I ask, "But won't this allow heat gain into the window cavity/structure," they downplay this concern or issue. I feel firmly about it though, and prefer the film to be installed on the exterior so that radiant heat energy simply bounces/reflects right off the film and doesn't even enter into the first pane of glass to begin with. If the film is installed on the exterior of the window, and the mirror is facing away from the house, then this heat energy will just bounce off and not enter even the first pane of glass. Is this not correct?

I am also being told that the window film manufacturers have largely discontinued exterior reflective films because they can't stand up to outdoor conditions.

What is true or false here?

While it may be true (but I am skeptical) that "modern" windows are "made" to withstand heat energy getting into them, why would I want to subject my windows to that added stressor and gamble on that?