Discontinuous surface-treated submicron-diameter carbon filaments are effective for use as an interlayer between continuous carbon fiber laminae in a nylon-6 matrix composite for enhancing the loss tangent (0.2 and 1.0 Hz) under flexure that involves bending of the fibers, without significant decrease of the flexural storage modulus or the tensile modulus ol strength in the fiber direction. The surface treatment is oxidation using ozone. Without treatment, the filaments are not effective. The treated filaments amount to 0.64 vol.% of composite; the interlayer thickness is 77 mum. A viscoelastic interlayer is even more effective than the treated filament interlayer for enhancing the loss tangent, but the accompanying decrease in storage modulus is much more. The loss tangent for composite with viscoelastic interlayer decreases upon heating, so the loss modulus for this composite is less than that of the composite with treated filament interlayer at greater than or equal to 50 degreesC.