2 - 4 pcf · NMFC density scale
The rating for freight at 2 - 4 pounds per cubic foot on the current 13-band NMFC density scale. Typically mattresses, molded plastic parts, light fixtures.
Class 250 covers 2 - 4 pcf. Mattresses, molded plastic parts and light fixtures live here. At this density you are essentially buying trailer space, so anything that compresses, nests or disassembles is worth compressing, nesting or disassembling before it ships.
Worked example. A standard pallet: 48 × 40 × 48 in, 160 lb. That is 53.3 cu ft and 160 lb → 3.00 pcf → class 250. Run your own numbers →
Band edges are inclusive at the bottom, exclusive at the top: exactly 2 pcf is class 250, but just below it the class gets more expensive — 1.99 pcf rates class 300. A few pounds of packaging or an inch of pallet height can move a borderline shipment across that line.
Freight class runs from 50 (densest, cheapest per pound) to 400 on the current density scale. Class 250 is band 11 of 13.
Either side of this band: denser freight (4 - 6 pcf) rates class 175, which is cheaper; lighter freight (1 - 2 pcf) rates class 300, which costs more.
The full table is on the freight class chart, and the calculator works out density and class from your dimensions, including multi-pallet shipments.