Thin iron/steel sheets.

[Dan Howard]

First of all, economic. Do we know how Romans made 0,5mm iron strips? We don't.

We have examples of scale armour made from 0.5mm plate from all over the world dating from the Bronze age onwards. We have metal foil many many times thinner dating from the Bronze Age onwards.

Sim and Kaminski tried 6 different techniques and all they could do was 4mm sheet (from ingot) which is 4x times thicker than remains and it has forging sings. But does it mean that segmentatas and scales were brought by aliens? Of course not. Romans had to had somekind of XXX kg hammers or rollers becasue otherwise they wouldnt be able to produce so thin sheets.

The Romans didn't need any magical technology. We know that many cultures before the Romans were capable of producing 0.5mm or even thinner metal plate.