What is "cuprammonium rayon"

Merriam-Webster defines Cuprammonium rayon as "a rayon made from cellulose dissolved in cuprammonium solution".

It is produced by making cellulose a soluble compound by combining it with copper and ammonia. The solution of this material in caustic soda is passed through the spinneret and the cellulose is regenerated in the hardening baths that remove the copper and ammonia and neutralize the caustic soda. Cuprammonium rayon is usually made in fine filaments that are used in lightweight summer dresses and blouses, sometimes in combination with cotton to make textured fabrics with slubbed, uneven surfaces.

The fabric is commonly known by the trade name "Bemberg", owned by the J.P. Bemberg company. The fabric may also be known as "cupro" or "cupra". Also as "ammonia silk" on Chinese fashion retail websites.