I found this little piece of infomation by the greek historian Ammianus Marcellinus describing the clibinarii cavalry of Shapur II
All the companies were clad in iron, and all parts of their bodies were covered with thick plates, so fitted that the stiff-joints conformed with those of their limbs; and the forms of human faces were so skilfully fitted to their heads, that since their entire body was covered with metal, arrows that fell upon them could lodge only where they could see a little through tiny openings opposite the pupil of the eye, or where through the tip of their nose they were able to get a little breath. Of these some who were armed with pikes, stood so motionless that you would have thought them held fast by clamps of bronze.
Hope this helps.