Imported goods can sit inside the United States for months without a dollar of duty being paid. The device that allows it is the bonded warehouse, and it works by separating arrival from entry.
Duty falls due on entry, not on arrival
Customs duty becomes payable when goods are formally entered for consumption in the domestic market. That is a paperwork event, not the same thing as unloading a container at a pier.
A bonded warehouse lives in that gap. It holds cargo under customs control after landing, so goods are physically in the country but have not legally entered commerce.
The importer pays when it withdraws stock, and only on what it withdraws. One shipment can leave the warehouse in pieces across a long stretch of time.
The bond is what makes customs comfortable
The warehouse operator posts a financial guarantee covering the duty that would be owed on everything stored. That bond is why the goods are allowed out of the port without payment.
In exchange the operator accepts inventory obligations: recorded receipts, recorded withdrawals, and records that customs can audit against the physical stock on the racks.
Shortages are the operator's problem. Goods that cannot be accounted for are treated as having entered the market, and the duty becomes payable regardless.
Cash flow is the actual product
Paying duty on a full container ties up capital until the last unit sells, which for slow-moving stock means months of money sitting still.
Deferring the payment to the moment of withdrawal lines the outlay up with revenue instead. On high-duty categories that timing difference is worth more than most discounts a buyer could negotiate.
Storage is not free, so the arithmetic only works above a certain duty rate. Importers use the option where the financing saved comfortably exceeds the warehouse fee.
Goods can leave without ever entering
Stock held under bond can be shipped onward to another country straight from the warehouse, and no domestic duty is ever assessed on it at all.
That turns an American port into a staging point for a wider region. A single arriving shipment can be split between domestic buyers, who trigger duty, and foreign buyers, who do not.
Limited handling is usually permitted under bond, such as sorting, repacking and labeling, so goods can be prepared for whichever market takes them without losing their status.
Foreign trade zones extend the same idea
A foreign trade zone offers comparable deferral inside a designated area, but with wider permissions, including manufacturing that changes what the goods actually are.
When imported components are built into a finished product there, duty is assessed on the form in which the goods leave the zone rather than on the parts that went in.
Both rest on one point: customs territory is a legal status rather than a line on a map, and goods can be physically present without being inside it.