Near infrared rays have wavelengths between 700nm-1400nm, accounting for 47% of sunlight. Far infrared rays have wavelengths between 4-16 micrometers, accounting for 51% of sunlight. Far infrared rays can penetrate 3-5cm into the body and have various health applications such as reinforcing the immune system, improving metabolism, and slowing the aging process. Far infrared emitting materials absorb sunlight or artificial light and re-emit it as far infrared rays, with common materials having peak emission wavelengths between 5-20 micrometers.