Sounds a tad too fancy? And why not, after all, these are the bespoke versions of regular envelopes that often boast sturdier materials and custom designs. Technically speaking, these are also known as paperboard pockets or paper sleeves. They are usually very upmarket to look at and solve the purpose of carrying cards and other collaterals of significance inside them. You could enclose packing slips, return slips, and other important papers in these. Depending upon need and design, these bear openings on one or two sides.