Polymeric structures produced with a controlled number and distribution of small, closed cells. The polymeric structures are characterized by an opaque, whitening appearance attributed, at least in part, to the distribution of closed cells and thus, at least in part, to light scattering resulting from the distribution of small, closed cells or voids. The light scattering thus provides an enhanced whitening effect. The whitening effect may be uniform or non-uniform along the length and width of the structure.