School Smart Kraft Envelope with Clasp, No 55, 6 x 9 Inches, Pack of 100 Large mailing envelopes are made of 28 lb heavyweight kraft stock and have wide seams for security. The deeply gummed flap has a reinforced eyelet to receive the double prong metal clasp. Ideal for storing or sending important paper work A great organizational method for school, home or work setting A must have for school administrators, lawyers and HR representatives