Open Side Booklet Envelopes, 9″ x 12″, 28#, White, Side Seams, Pressure Sensitive Seal (Box of 500). 9″ x 12″, Open Side Booklet Envelope, No Window, Western Sulphite, White Sulphite Paper, Paper Color: White, SFI Certified, Vellum Finish, Side Seam, Flap Down, Kwik-Tak, 500 Qty / Box, 500 Qty / Ctn, 20.5 lbs.