As I wrote, they (Inkpress) makes *2* different Duo lustre/SG papers.
The first is an RC
Inkpress Luster Duo is a premium high-resolution, double sided, resin coated, microporous, bright white photo grade paper designed for the highest quality color images on both dye and pigment inkjet printers. Its new ultra absorbent coating allows UntraChrome and other pigmented inks to dry instantly, preventing puddling and black (shadows) highlighting or laying on top of the surface of the paper.
The other one isn't but is an alpha-cell paper. Or are you fixed on a cotton paper?
My client saw the photo rag pearl and she likes the paper so much for her custom made book. And she doesn't really feel like the RC would satisfy what she wants.