Known. The armour was made of small stone plates.
The plates were found in and around the tomb of Qin Shi Huang, in Shaanxi Province. He ruled from 221 to 210 BC, and the armour is about 2,200 years old. More than 600 small limestone plates were found, joined with bronze wire. More stone armour, and the tools used to make it, turned up by the Wei River at Xinfeng, and at a site in Xianyang, the Qin capital. The Xianyang dig found 32,392 pieces, including unfinished plates. The stone armour copied the look of real armour, but it was made for tombs, not for battle, because stone lasts longer than leather. The stone was brought from far away.
The page does not say what is still argued.
https://www.ancient-origins.net/news-history-archaeology/qin-dynasty-stone-armor-0018733