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Performance metrics & physics

Far-Infrared (FIR)

Far-infrared (FIR) is the lowest-energy infrared band, beyond about 25000 nm, primarily associated with thermal radiation from objects rather than sunlight.

FIR is essentially heat radiation from warm objects (including human bodies). Solar radiation in this band is negligible at Earth's surface, so FIR is not relevant to automotive solar films.

In some health-tech applications (FIR saunas, FIR-emitting fabrics) the band gets attention. For window film, FIR is a background term — not a design target.

We mention it for completeness in technical literature, but it's not a meaningful spec to compare films on.