Product Information: Internal Dimensions: 266mm (length), 353mm (width), Fold Lines allow for increasing width to 35-50mm to accommodate contents, Royal Mail Small Packet size when expanded, Integrated Documents Enclosed Wallet. Packaging Shack’s Envelopes are great for protecting books and DVD’s etc. in transit. Made from a rigid card, these envelopes have pre-defined folding lines to allow the envelope to accommodate contents up to 35mm 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.