 A Predator bio-mask increases its ability to see in a variety of spectra, ranging from the low infrared to the high ultraviolet, and also filters the ambient heat from the area, allowing them to see things with greater clarity and detail.While they are capable of breathing Earth's atmosphere, the creature in "Predator 2" is seen using a breathing mask after losing his helmet (although this Predator had just been shot multiple times and may have, therefore, not been operating at his full potential.A second possibility is that it was used to filter out impurities in the air— exhaust and such—which would not be found in more natural environments).