Yes, it is usually copper paper.

Most of the special papers used for certificates are high-end. If the coated paper is too ordinary and not graded well, and the coated paper is too large, the certificate will really be more.

Copper paper is a high-grade printing paper made by coating white paint on base paper. Mainly used for printing high-end book covers, illustrations, color pictures, various exquisite product advertisements, samples, product packaging, trademarks, etc.