Product Information: 4 sizes available in boxed quantities of 100Peel and Seal Closure. Fold Lines allow for increasing width up to 80mm to accommodate contents, Royal Mail Small Packet size when expanded, Manufactured from rigid corrugated cardboard. Packaging Shack’s Rigid Book Envelopes are great for protecting books and DVD’s etc. in transit. Made from a rigid cardboard, these envelopes have pre-defined folding lines to allow the envelope to accommodate contents up to 30mm thick at the expense of some of the envelopes height and width. The envelopes are sealed using a peel and seal strip to ensure it remains sealed during transit.