Strain wave propagation velocity in fibre materials is a primary consideration in the design of body armours for ballistic protection. In this paper, we compare the strain wave propagation (sonic) velocities and moduli of parallel and twisted ballistic fibre strands (yarns) derived from quasi-static tensile test and strain wave pulse test. In parallel multifilament yarns, the individual fibres behave independently from each other, and the yarn sonic velocities and moduli derived from the two test methods match each other very closely. In yarns with a twisted structure by twisting multifilament yarn or by spinning short fibres, fibres in the yarns are compressed against each other and fibre-to-fibre friction plays a significant role. Consequently, the yarn sonic velocities and moduli determined by the strain wave pulse method are significantly greater than that derived from the quasi-static tensile method.