The technical explanation:

Lets look at some films tested at the iso9050 2003, NFRC 300 2003, and prEN 410 standard.

look at a film like VK-70. at 1000nm it passes less than 10%, tapers to less than 2% at 1200nm and stays below that up to 2500nm. yeah.. it is really rejecting heat is the form of IR. True that is still transmits 73% of the Visible light and less than 1% UV. Putting the true heat rejection (only Film, no glass subtractions) at >54%.

Lets look at Panaroma Sterling 70 . At 1000nm, it is transmitting over 60%, tapering to over 25% at 2500nm. Still alowing over 70 Visible light transmission.

Now lets look at Solar Gard Stainless Steel 30. At 1000nm it transmits about 38% and dips steady at 28% to 2500nm. It gains a fair amount of heat reduction by reducing the Visible light to 30%. TSER of 53%.

The trick to impressing people is to use only a red IR lamp to show the film performance. If you took out the red lamp and put in a white IR ulb, you would see a closer real life comparison of the films.

I'm not saying that a conventional film doesn't work, I'm just saying that a tinted metalized film blocks a different portion of the "heat gain". If you really wanted to get into it, we could look at the amount of heat gained in the winter by a Spectrally selective film through visble light, then add the insulative value for interior IR reflection and come to roughly 35% winter heat gain. (We would have to look beyond conduction and convection of the glass surface and air currents) Who cares about that.

What does it look like, does it do what I want it to do? Do I want to do business with you?

I've sold against V-Kool, Huper and Vista Spectra Select left and right. Some poeple like the reflection, some people like no reflection, some people want clear, some people want tinted, some people want the cheapest fillm they can get, some people want only the best. Every film has it's pro's and cons.

One problem that the film industry faces is truth in numbers. Every manufacturer publishes numbers that boast their films and omit numbers hurt them.. V-Kool and Huper are going to push IR. Metalized films will push TSER. Low E Films will push U Value. Most companies do not publish SHGC. Most people get sold on the R and U values of windows. Most films don't even have these measurements because to get a good R and U value requires a reduction of conduction, not radiation. Films block RADIATION. Not to mention the building codes rarely even compensate for the performance increases that a film provides when considering glazing requirements.

There are several standards that do measure IR. ISO 9050:2003, NFRC 300 2003, or prEN 410. These may not be the adopted standard, but they do mesure IR in the total calculation.

From ISO:

ISO 9050:2003 specifies methods of determining light and energy transmittance of solar radiation for glazing in buildings. These characteristic data can serve as a basis for light, heating and ventilation calculations of rooms and can permit comparison between different types of glazing.

ISO 9050:2003 is applicable both to conventional glazing units and to absorbing or reflecting solar-control glazing, used as glazed apertures. The appropriate formulae for single, double and triple glazing are given. Furthermore, the general calculation procedures for units consisting of more than components are established.

ISO 9050:2003 is applicable to all transparent materials. One exception is the treatment of the secondary heat transfer factor and the total solar energy factor for those materials that show significant transmittance in the wavelength region of ambient temperature radiation (5 microns to 50 microns), such as certain plastic sheets.