Vambraces protect the forearm. In the 14th Century, some of the richest knights had steel vambraces, but many were of leather, which might have been boiled for hardness or strengthened with metal studs or splints.
My vambraces are splinted leather, with metal strips riveted into the cuff.
At the elbow, they are tied onto the gambeson with points and laces.
This is a picture of 14th Century vambraces from the funeral brass of John Foxlay, dated 1378.
Unlike his upper arm defenses, which appear to have plates on the outside and straps on the inside, the vambraces go all the way around.