Our strongest mailing bags are comprised of 90 (354 gauge) micron polythene, a much tougher and more durable material than that of standard mailing bags. All of these heavy duty bags are co-extruded, which means that several layers of film are extruded together to create a more robust bag. Kite offer six sizes, all of which comply with Royal Mail's PiP guidelines, enabling you to accurately calculate your mailing costs. The white outer and black inner creates a 100% opaque product that will fully conceal the contents from view for total confidentiality and security. Due to the strength of the construction, the polythene is also highly tear-resistant to further promote the safe transportation of goods. For heavier or higher value items, Kite's thick polythene mailing bags are an appropriate packaging choice that maintains optimal cost-effectiveness. The bags feature a strong self-adhesive peel and seal strip on a 40mm lip.