Actually, Michele, the term "paper" is extremely misleading.
Here's what the Wallis archival paper is made of:
Base Paper:
Meets Library of Congress starndards for permanence; archival 100% virgin cotton rag, acid free and buffered; developed in consultation with art material conservation experts from the National Gallery and Smithsonian;
Coatings:
pH Neutral archival adhesive; Wallis proprietary neutral pigmented coating;
Grit:
Inert white aluminum oxide.
The paper feels like vinyl, and is coated on both sides, gritty on one side. You can literally submerge the paper into water. It can be underpainted with or without stretching or mounting on panel (as I do), in water-based pigment washes, pastels/acetone (like my
blue drawings), mineral spirit or rubbing alchohol washes, or oil, without ever buckling from moisture.
I really love this stuff.