Blow-molded plastic structures may include a plurality of depressions and the depressions may have different characteristics depending, for example, upon the particular configuration of the depression. For example, a depression may have an elongated length and it may have increased strength along its length. The depressions may be arranged into a pattern in order to take advantage of particular characteristics of the depressions. For example, the depressions may be arranged to maximize the strength and/or minimize the weight of the structure. The depressions may also be arranged to create a structure with generally uniform characteristics. Significantly, the depressions may be arranged into a number of different patterns depending, for example, upon the intended use of the structure. For instance, the depressions may be arranged into a pattern with one or more rows and columns, and the depressions may be disposed in particular positions or orientations within the rows or columns.