They can be washed in a washing machine with a mild detergent and seem to last forever. Dust Bunny is available from Light Impressions, University Products and Gaylord. Dust have been okayed for use in libraries and archives by the Library of Congress and the National Archives. Neither leave a residue on books, boxes or shelves. However, after prolonged use the user's hands feel sticky since some of the chemical come off on one's hands and then dust adheres to the fingers.
Dust is more economical for large scale dusting projects.
And since they are disposable, they would be a better choice for use in environments where mold might be present. However, I like to use Dust Bunny in our book repair shop and in the archives, because they are softer and one's hands stay cleaner.