Open Side Booklet Envelopes, 6-1/2″ x 9-1/2″, 28#, White (92% Brightness), Vellum Finish, Side Seams Under (Box of 500). 6-1/2″ x 9-1/2″, Open Side Booklet Envelopes, 28#, White (92% Brightness), Vellum Finish, Two Side Seams Under.