HPD 2.1 has three approaches for creating an HPD, they are:
Nested Materials Inventory with Material-level thresholds. This is the approach used in HPD 2.0 in which contents are reported first at the materials level and substances are then itemized within each material. Thresholds are established for each separate material and these thresholds determine which substances must be listed under each material.
Nested Materials Inventory with Product-level threshold. This is similar to the first approach in that contents are reported first at the materials level and then substances are itemized within each material. In this approach, a single threshold is established for the entire product and this threshold is used to determine which substances must be listed for any of the materials.
Basic Inventory with Product-level threshold. This approach does not identify materials and creates a single list of all substances in the product. It uses a single threshold for the entire product.
Nested materials inventories often are most appropriate for complex assemblies with many component parts. In many cases, the HPD can be created from data provided by suppliers for their materials For product lines with many variations, the nested approach can be most efficient, since individual materials can be switched and replaced more easily to reflect differences in color, fabric covering, etc.