About the "Babr-e- Bayan" famous armor of Rostam, since there are so many conflicting opinions and and yet the substance of this armor,is one of the puzzles of Shahnameh. Some believe that "Babr-e- Bayan" is made of dragon skin,skin of Akvane Div, leopard or cheetah skin or tiger skin (known predatory animals), But in my opinion none of the above is true. Based on the evidence discussed in the paper, the background of wearing the beaver skin, according by Avesta, come back to Anahita and as the "Babr" in the Avesta is no doubt refers to the beaver, "Babr-e- Bayan" Rustam was also made ​​of beaver skin, Perhaps one of the reasons that Rostam is known as Segzi, in addition to his assignment to the Sistan, has been wearing a beaver skin ("Babr-e- Bayan") in the wars, Because there was no reason that only the enemies of Rustam have been used this word and his friends did not use this word. In the other hand why Rustam frankly has been hated because of addressing him by this epithet? In this essay according by evidences, it has obtained this conclusion that Sagzi, in addition to his assignment to Sistan, this word had been used for contempting Rustam as the meaning "one who lives like a dog". using this word in this meaning because of Rustam is wearing the Babr-e Bayan that is made of beaver skin. "Bayan”, the attribute of "Babr" apparently would be a distortion of the "Bghan" means "godly", because the background of wearing the beaver skin as it was said,come back to Anahita.