Specifies the type of commodity product.
For coal see http://www.fpml.org/coding-scheme/commodity-coal-product-type for values.
For metals see http://www.fpml.org/coding-scheme/commodity-metal-product-type for values.
For bullion see http://www.fixtradingcommunity.org/codelists#Bullion_Types for the external code list of bullion types.