Infrared cinematography opens up a whole new spectrum of light not visible to the unaided eye. This has the potential to give otherwise ordinary scenes a surreal and dream-like appearance.
In general, foliage, clouds and skin reflect more near infrared light and appear lighter, whereas clear blue skies and most tree trunks appear darker. Smooth water surfaces also become darker, but this is primarily because they are reflecting a darker sky. The overall effect helps manage contrast in otherwise harsh midday light, similar to how using a red filter enhances contrast with monochrome imagery. With studio work, the skin on models will appear smoother and ghostly white, but veins might also appear darker and more pronounced if they’re close to the surface. With clothing, red pigments will often become brighter than white pigments were with visible light.
See full details and examples of Infrared Cinematography in the RED 101 Article: Exploring Infrared Cinematography