Cardboard Envelopes Peel and Seal Strong Board Packaging Postal Mailing Shipping Postal Royal Mail Large Letter Posting Envelopes (334x234mm), 10 Envelopes) : Amazon.co.uk: Stationery & Office Supplies
Strong Mailing Envelope - C4 (230mm x 325mm x 90 micron)
GoSecure Envelope Extra Strong Polythene 460x430mm Opaque (Pack of 100) PB28282