An explanation of Foreign Trade Zones and how exporters can utilize them. This information is from "A Basic Guide to Exporting" provided by the U.S. Commercial Service to assist U.S. companies with exporting.
Last Published: 10/20/2016
As an exporter, your company should also consider the customs privileges of U.S. foreign trade zones (FTZs). These zones are domestic U.S. sites that are considered outside U.S. Customs territory and are available for activities that might otherwise be carried on overseas for customs reasons. For export operations, the zones provide accelerated export status for purposes of excise tax rebates. There is no issue of drawback because duties are not collected when the goods are in the FTZ. For import and reexport activities, no customs duties, federal excise taxes, or state or local ad valorem taxes are charged on foreign goods moved into FTZs unless and until the goods or products made from them are moved into U.S. Customs territory. Thus, FTZs can be profitable for operations involving foreign dutiable materials and components being assembled or produced here for reexport. Also, no quota restrictions ordinarily apply to export activity.

As of January 2014, there were more than 200 approved FTZs in communities throughout the United States. These facilities are available for operation involving storage, repacking, inspection, exhibition, assembly, manufacturing, and other processing. The value of merchandise handled by FTZs exceeds $640 billion. 

Additional details (as of February 24, 2014) can be found at http://1.usa.gov/1zucnDd. Information about the zones is available from the zone manager, from local U.S. Commercial Service offices, and from the Foreign-Trade Zones Board. Additional information is available at http://ia.ita.doc.gov/ftzpage