Stretch Metallic Panne' velvet

Based on where the seams are, it appears the fabric used was dress fabric as opposed to bedding fabric.

Looks like washed silk to me.

It's probably a drapery fabric which is usually used. Seams are
normal. Bedding fabric is sheeting, used for sheets, and hard to find
these days.

Looks like a silk to me too or maybe a sateen.

Where is the original picture from?

After Five Designs

It's either a silk or a velvet. Neither is a good choice for a duvet cover. The entire point of a duvet cover is washability - EASY washability.

I immediately thought Panne' velvet, too, before reading any comments. But the area below the seam looks like a different fabric, possibly silk or satin, or maybe just the nap is running a different way.

It would be dry cleanable and for homes with no pets and no kids in that bedroom, it would be fine (and gorgeous).

https://www.pier1.com/essex-silver-quilt-%26-sham/PS68350.html?st=Essex%20Silver