Pranamaya kosha; Pranamaya means composed of prana, the vital principle, the force that vitalizes and holds together the body and the mind.
It pervades the whole organism, its one physical manifestation is the breath.
As long as this vital principle exists in the organisms, life continues.
Coupled with the five organs of action it forms the vital sheath.
In the Vivekachudamani it is a modification of vayu or air, it enters into and comes out of the body.