As explained earlier, we expect that product design will take place in four, roughly sequential steps. First, we will identify needs; second, we generate ideas to fill these needs; third, we select the best ideas; and last, we consider manufacturing. So far, we have discussed identifying needs, generating ideas to fill these needs, and choosing a shorter list for further study.

We now want to select the best ideas for further development. In some cases, we will have only one or two clear choices. In most cases, we will want to select from five or fewer possibilities, simply because the amount of work required for further development is so substantial. In selecting between these few products, we can identify two separate situations. In the first, we can compare products using only technical criteria drawn from chemistry and engineering. In the second, we must compare products not only on a technical basis, but also using more subjective criteria, like “comfort” and “safety.” How we proceed in product selection depends on which of these two situations we encounter.

In the first situation involving only technical criteria, we already have the tools for selection from our technical training. In particular, we have a background in thermodynamics and so can calculate any chemical equilibria or heats of reaction suggested in our product development. We also have a background in kinetics, including an understanding of reaction rate constants and how these change with temperature.