The Health Product Declaration (HPD) offers two overall ways to organize and display the content inventory: Basic and Nested. Both are LEED-compliant. The Nested inventory is preferred by HPD users because it provides more granular data on a product. (This article focuses on what the difference is between the inventory methods. For more on why, see Which content inventory method is better, Basic or Nested?)
- In the Nested Materials Inventory, contents are reported first at the “material” level and then at the “substance” level. That is, materials are listed, and then specific chemicals, are itemized with each material. For example, carpet backing is a material, and in a nested inventory a manufacturer may list several substances within it such as polypropylene and limestone. Carpet fiber may comprise another material, and a manufacturer may list several substances within it, such as nylon and dye. The HPD with a nested inventory will show the percentage weight for each material, and then the breakdown within that material of the weight of each substance.
- In the Basic Inventory, contents are reported only at the “substance” level, regardless of the material structure of the product. Using the same example, the carpet would list polypropylene, limestone, nylon, and dye, and would assign a percentage weight relative to the overall product for each one.
The Nested versus Basic inventory difference is illustrated here:
In addition, manufacturers must choose on their HPDs to establish thresholds at a Material or at a Product level. Thresholds—such as 100 ppm or 1,000 ppm—establish reporting requirements for substances on the HPD. If a 1,000 ppm threshold is selected, the manufacturer must disclose all ingredients above that concentration.
Choosing a material-level threshold means that the manufacturer must disclose all ingredients above that concentration in each material within the overall product. Choosing a product-level threshold means that the manufacturer must disclose all ingredients above that concentration in the entire product.
This means there are three possible approaches for creating an HPD, each of which provides a different level of detail in its information. They are listed here, from most to least detailed:
- Nested Materials Inventory with Material-level threshold: Thresholds are established for each listed material. Substances within each material are reported if they are above the established threshold for the material.
- Nested Materials Inventory with Product-level threshold: A single threshold is established for the entire product. Substances within each material are reported if they are above the product threshold.
- Basic Inventory with Product-level threshold: A single threshold is established for the entire product and all substances that are above the product threshold are reported. No material level information is provided.
All of these methods are LEED compliant, but they result in different levels of information qualify. For more on why these differences matter, see Which content inventory method is better, Basic or Nested?