Many publications are mailed in polybags, but they are used for other types of mail as well. They are usually less expensive than envelopes and their transparency allows the contents to be viewed before the package is ever opened.
For many applications, the item (e.g. magazine or catalogue) is physically addressed before being placed into the polybag. However, as illustrated in the different options below, this is not always the case. Frequently, lead sheets are used or a label is placed directly onto the polybag.