Crescent Select:

Produced using only 100% virgin alpha-cellulose
fibers for lasting quality.

Acid-free and lignin-free for maximum artwork protection.

Above is from their website -- so I would say that its archival properties are not as good as a cotton based board.

Also from their website about their cotton based board:

Cotton is nature's purest form of cellulose. It is inherently free of lignin, acid and other non-cellulose contaminants found in wood pulp. Cotton fiber pulp is reliable, sturdy and far superior to bleached, chemically processed wood pulp used to produce other conservation boards.

And then on the same page they state: "Only cotton should touch the art"