Cake Decorating Tools & Supplies

What is that material and how to use it?

Hi all,

Dose anyone know what is the material of the gold big sheet on the top of this cake and what is the technique to use it?

https://www.instagram.com/p/CLkWD1ch6Ty/?igshid=1vl6ljwrz3xcm

Thanks,in advance

Koki cakes