Some sort of packaging will normally be a prerequisite for carrying commodities as general cargo, especially in break bulk. Packaging has at least three functions:

(a) To protect the goods;

(b) To keep a consignment together;

(c) To prevent the goods from damaging the environment.

Transport usually subjects the cargo to mechanical forces (shocks, vibrations, pressures) and/or climatical forces (temperature, moisture). At least for a conventional shipment, the packaging needs to be strong enough to withstand the rigorous of stowage and multiple handling.

Goods which are not packed properly may damage other goods in the same transport. In such cases the shipper may be liable. Paper and carton are traditionally mostly used in local transport, where the risk of damage is usually smaller. Plastic and especially jute are used to produce bags. Bags are commonly used to pack traditional bulk commodities in small quantities, like cement, sugar or grain. Wood is still common to make cases or crates. Drums and barrels are made of metal or plastics and are used for transport of liquids in small lots.

courtesy: http://generalcargoship.com