Open Side Booklet Envelopes, 10″ x 13″, 28#, White, Side Seams, Pressure Sensitive Seal (Box of 500). 10″ x 13″, Open Side Booklet Envelope, No Window, Western Sulphite, White Sulphite Paper, SFI Certified, Vellum Finish, Side Seam, Flap Down, Kwik-Tak, 500 Qty / Box, 500 Qty / Ctn, 27 lbs.