Linothorax design/construction

[PMBardunias]

Here's the translation if it helps you see where they got the notion of quilting from:

8] Since the rider is seriously imperilled in the event of his horse being wounded, the horse also should be armed, having head, chest, and thigh pieces: the last also serve to cover the rider's thighs. But above all the horse's belly must be protected; for this, which is the most vital part, is also the weakest. It is possible to make the cloth serve partly as a protection to it. [9] The quilting of the cloth should be such as to give the rider a safer seat and not to gall the horse's back.

He mentions guard for the "auchena" the back part of the neck and this reminds me the linothorax.

The fact that it protects the riders face makes the combination of Boetian helm and neck guard seem like a medieval sallet and bevour. There are many images of steppe peoples of later dates with high collars, but this sounds almost like the collar of a Mycenaean armor. I agree that the arm guards are most likely bands of metal- otherwise the metal armpit guard would offer more protection than that given the arm, which is unlikely.

Odd that there are no images of this, unless it is like De Saxe's work and what he recommends is so idealized that it will not be found in service in any numbers.