The DL envelope is a type of envelope commonly used for mailing letters, documents, brochures, and other small items. It measures approximately 110 mm x 220 mm (or 4.3 inches x 8.7 inches) and is designed to accommodate A4 paper folded into thirds.

A "do not bend" DL envelope is designed to protect the contents from being bent or damaged during the mailing process. These envelopes are typically made from strong, rigid materials such as cardboard or thick paper to provide extra protection for the contents.

To ensure the contents are protected during transit, it's important to securely place the items inside the "do not bend" envelope and properly seal it. Additionally, It's important to note that while a "do not bend" envelope can provide extra protection for your mailing, it does not guarantee that the contents will arrive undamaged.