A bill of materials (BOM) is a comprehensive inventory of the raw materials, assemblies, subassemblies, parts and components, as well as the quantities of each needed to manufacture a product.  it is the complete list of all the items that are required to build a product.It is a list of the items needed to create a product as well as the instructions on how to assemble that product. Manufacturers that build products start the assembly process by creating a BOM. A bill of materials (BOM) is a structured list identifying all materials and components required to construct a product, as well as the instructions for procuring and using the materials.