Protective helmet cap

A method of configuring a helmet cap, the method comprising:

• determining one or more target resonance modes;
• and
• configuring one or more of a size, a material, and a mass of one or more padded segments of a plurality of padded segments, such that the one or more padded segments are tuned to suppress, upon impact with an object, vibrations within one or more ranges of frequencies corresponding, respectively, with the one or more target resonance modes,
• wherein the helmet cap comprises an outer shell designed to attach to a helmet, wherein the outer shell comprises the plurality of padded segments and a plurality of indentations, wherein at least one indentation of the plurality of indentations is disposed between at least a pair of padded segments of the plurality of padded segments, and wherein the one or more ranges of frequencies is defined, at least in part, by the configured one or more of a size, a material, and a mass.