 Previously, the rubber particles were considered as the main contributor to the increased energy absorption.It was proposed that rubber particles might gather around crack tips under tension and impede the growth of crack, or the contraction of rubber particles induced the decline of glass transformation temperature of the matrix.Nevertheless, experiments showed that the energy absorbed by rubber particles made up only 10% of the total energy, and the decrease of glass transformation temperature caused by rubber was only around 10 K, which was not enough for the matrix to yield at room temperature.