Vikings, like The Last Kingdom, plays fast and loose with history, especially when it comes to material culture (hair, clothing, weapons, etc). It goes for a Game of Thrones-inspired aesthetic that looks noticeably different from what archaeology tells us about the Viking age. It's really laughably bad in places, and this is one of them. I have no idea what that armor is meant to be; it looks like papier mache and about as effective. My guess is it's cheap to make and looks cool to the director.

The reality is that there weren't that many types of armor available in the 9th century. Whether a Viking, a Frank, or a Saxon, the best protection available at the time was a mail shirt and an iron helmet. Both of these were expensive, which tended to limit them to landowners and the semi-professional soldiery (often one and the same). The poorer folk had to make do with a shield.