An impact energy absorptive structure is made of usual plastic materials suitable for molding processing, and is designed to suit different degrees of impact loading anticipated in various applications. The impact energy absorptive structure is composed of a base member 11 and protruding rib members including long and short members, in which the proportion of the cross sectional area of the long rib members is between 0.3 to 0.8 of the total cross sectional area of the rib members. Other design modifications can be made readily to customize the impact resistance of the impact energy absorptive structures.