In examining various foam-core materials used in sandwich construction, we see that the core-shear modulus, G c , varies almost linearly with the foam density, ρ c . Since there is a continuous spectrum of shear moduli commercially available within a sizable range of densities, G c can be considered as a continuous variable and not limited to discrete values for a given material. For example, consider closed-cell PVC foams [1, 2]. One can plot the properties as in Figure 13.1. For these materials, the relationship between G c and ρ c is almost linear. Regardless of this relationship, however, is the important conclusion that one can select any value of G c as a variable in a foam-core sandwich construction just as one may select values of t f and h c . This has been utilized by Vinson [3–5] in the optimization of foam-core sandwich panels subjected to in-plane loads. Typical foam core properties. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780203737101/ec16b8ec-dde3-4c51-a54e-255fa17943d6/content/fig13_1.tif"/> (Reprinted from Reference [8].)