These heavy duty, protective board back envelopes from blake use 1000 micron backing board and heavyweight face paper to ensure your bendable items are protected in transit.the super thick manilla backing board provides extra rigidity while the 120gsm white face paper protects the contents and gives your mailer a clean, crisp finish. Closes with a strong peel and seal flap.ideal for books, certificates, legal correspondence, magazines and more.. Heavy duty board back pocket envelopes. Provides rigidity and protection for bendable items. 1000 micron manilla board 120gsm white paper. Strong peel and seal flap closure. Size c3 450 x 324mm. Pack of 100