Paper needs to weigh at least 7 lbs per 500 sheets for a single sheet self-mailer. For a multiple sheet self-mailer the requirement is 6.5 lbs per 500 sheets. Translation: 0.224 ounces per 8 1/2 X 11 sheet if it's a single sheet and 0.208 ounces per sheet for a multiple sheet mailer. Lighter papers require two tabs rather than one to hold them closed, doubling the cost of tabbing.

Using 70-lb. paper for single sheet mailers (or as the outside sheet on a multiple sheet mailer) qualifies the piece for automation compatible rates with a single tab.

Light or improperly tabbed paper jams postal service equipment. Since they process mail at a rate of 10,000 pieces per minute (166 pieces per second), jams not only cost the Postal Service money, but can also destroy several hundred pieces of mail before they can stop the equipment.