FIRs, which are also called Far (or Long) Infrared Rays, or IR-C (type C Infrared Rays) represent only a part of the electromagnetic solar spectrum. The FIRs are part of the waves that are naturally emitted by the sun and they are safe, beneficial and revitalising.

They are:

1. Infrared, meaning “under the red”, because their frequency can be found immediately beneath the one of the colour red;
2. Far, because they represent the furthest portion of the electromagnetic solar spectrum, approaching the wavelength of radio waves. The Far Infrared Rays are a portion of the electromagnetic spectrum that is invisible to the human eye, but it can be felt sensorially in the form of heat. FIRs (also known as IR-C rays) emit thermal radiation, have a wavelength of 4 μm-1000 μm and are able to transfer energy in the form of heat without the negative effects of radiation. In addition, they do not need air to transmit heat, because they propagate even in an absolute vacuum: this means that they do not heat the air, but only the bodies on which they are irradiated.

There are three types of infrared rays with different irradiance, efficiency and irradiance values:

• IR-A or NIR-A (type A Infrared Rays) or Short Wave Infrared Rays;
• IR-B or MIR-B (type B Infrared Rays) or Medium Wave Infrared Rays;
• IR-C or FIR-C (type C Infrared Rays) or Long Wave Infrared Rays, also called FIRs, which can be considered as the good part of the sun’s infrared radiation. In contrast, prolonged exposure to IR-A and IR-B can be harmful to living organisms. A living body absorbs and simultaneously radiates far-infrared waves because its water molecules and protein structures oscillate at the same frequency as the FIRs. Therefore, considering that living organisms are mostly composed of water, the action of FIRs on them facilitates purification and cellular metabolism in general.

Several studies claim that FIRs strengthen the immune system and improve the blood circulation process of skin, muscles and connective tissues by supplying more oxygen and nutrients. Far-infrared radiant elements are used to warm newborn babies in incubators in paediatric wards and are also widely used in other medical and therapeutic areas.