Abstract: The present invention relates generally to sizing compositions for fibers used in composite materials. More specifically, this invention relates to siloxane fiber sizing solutions comprising rubbery-polymers and their use in preparing composite materials. Using the sizings of the present invention not only improves the energy absorption of the composite materials made thereof, but also maintains the interfacial strength of composite materials. Particularly, the rubbery-polymers of the present invention are functionalized with chemical groups that react to the fiber surface and/or to the polymeric resin. In addition, because the rubbery-polymer is incorporated as one block of a block copolymer, it advantageously improves both, the interfacial strength and energy absorption.