Obviously we don't have much medieval armour around, though has anyone ever noticed it's thickness compared to later armour? (taking into account any corossion?)
I remember reading on here that the Avant harness had lames in the 1.6 mm region, while late period armours seem to have been thinner on average, except the breastplate/helmet. Though due to the increased use of firearms during the time, it would be logical to move the metal to the breastplate, like the "all or nothing" concept foremerly used for warships.

Alan Williams has published a table measuring maximum thickness vs. date for a hundred or so breastplates in his book ""The Knight and the Blast Furnace". Generally, armour slowly gets thicker from 1400 to 1650, but a big part of this is an increasing threat from guns.

The Avant harness is actually much thicker than 1.6mm in places; some of the frontal fauld lames reach 4mm or more through the center.