Water absorbs infrared radiation and beach scenes show that. Human flesh, foliage and other things reflect it. On the print it turned out grey. I was surprised. This additional layer is why filters are used.
Filters pass some light and absorb others.
With color film, a yellow filter is used which then stops exposure to the blue layer of the film and only allows the red, green, and infrared layers to expose- creating a false color image. Other color filters are used to expose other combinations of the layers. This allows only the red and infrared layers to have exposure, causing the IR effect. So if a person is photographed with the red filter and flesh reflects infrared light, the flesh will be white. Any color or object that does not reflect red light or IR radiation will be black.