para-Aramid fiber has well-oriented molecular chains and a structure with a large number of microfibrils. As a result, it has an excellent tensile strength and modulus and impact resistance [1]. Accordingly, a typical para-aramid fiber Kevlar? has been predominantly used as an anti-bulletproof material since 1971 when it was first developed by Du Pont Co. [2,3]. Once para-aramid fibers are used as a reinforcement in polymer resins, the resulting composites exhibit high mechanical properties compared to the composites with other organic reinforcements [4,5]. However, uses of para-aramid fibers or fabrics are somewhat limited due to their high cost. Therefore, it would be very desirable if an increase of the mechanical properties and a weight reduction of the resulting materials could be attained with a reduced amount of para-aramid fibers or fabrics.