A curable composition exhibiting excellent moldability without mold staining or delamination is provided, including an epoxy resin, a curing agent for the epoxy resin, and a polyphenylene oxide compound having a glass transition temperature between about 165.degree. C. and about 190.degree. C. The polyphenylene oxide compound may be provided as a melt blended mixture of two polyphenylene oxide compounds having distinct glass transition temperatures. The curable compositions may further include a bulk filler, and are therefore particularly useful as molding compounds encapsulation of electrical and/or electronic parts in transfer molding operations.