Compositions having improved gas/vapor barrier qualities are described. The compositions are composed of a substantially non-polar resin and a lamellar filler, the lamellar filler delaminating under high shear, to increase its aspect ratio. Also described are compositions composed of a non-polar thermoplastic resin filled with platelets of talc having an aspect ratio of at least 5; the platelets have an average aspect ratio of between 16-30 and a CIE whiteness index of at least 40.