Preferably hydrogenations or partial hydrogenations are carried out to modify the hydrocarbon resins.Hydrocarbon resin polymers and copolymers, such as styrene homopolymers, styrene copolymers, cyclopentadiene homopolymers, cyclopentadiene copolymers and/or terpene polymers, may be used alone or in admixture.A particular type of hydrocarbon resin that may be included in the skin layer is a saturat