ASTM D4168 outlines two methods for determining the shock absorbing characteristics of foam-in-place packaging materials. Method A uses a free-fall drop-test apparatus; Method B uses a shock test machine. Both methods are designed to simulate the way in which the foam will actually be used in a packaging application. That is, what you are measuring is actually transmitted shock.
In each test method, a certain thickness of cushioning material is placed around a weighed test block inside a package, and the complete package is subjected to a free fall drop (Method A) or a controlled shock on a shock machine (Method B). Because of the difficulty of accomplishing a perfectly flat free fall drop under Method A, however, Method B is often preferred. The static loading and maximum acceleration recorded for each test correspond to a point on a transmitted shock curve for the tested cushion thickness.