The coat of plates adds impact- and puncture-resistance to the chain mail hauberk. It is made of overlapping metal plates riveted to a leather smock. Coats of plates varied in design and length during the 14th Century. Some were a wide belt with suspenders, while others were like a vest or apron.
With the coat of plates turned inside out, you can see how the plates are arranged.
I modeled mine after the funeral brass of Sir John d'Abernoun the Younger,
who died in 1327. It shows a thigh-length coat of plates hanging down beneath the surcoat, but over the hauberk and gambeson. Seven visible rivets suggest seven plates per row, which is how mine is made.
Even using aluminum plates, my coat of plates weighs ??? pounds!