Please note that Circularity's proprietary, patent-pending Premium CO2 Cartridges are shipped under the U.S. Department of Transportation's (DOT) so-called Dangerous Goods (HAZMAT) safety license because of the pressurized liquid CO2 content that requires a signature on delivery. Each product box contains 25 steel mini CO2 cartridges weighing nearly 4 lbs (1.8 kg), which may add to the extra cost of HAZMAT-certified shipping.