The stability of polystyrene (PS) films on silicon oxide is improved by blending with poly-(styrene-block-methyl methacrylate) (PS-b-PMMA) having a short, adsorbing MMA block and long, dangling PS block (degree of polymerization N). Relative to PS (degree of polymerization P), hole growth velocity decreases by 5 and 17 times upon adding 0.05 volume fraction of PS-b-PMMA (phi) for N similar to P and N similar to 4P, respectively. In contrast to PS, holes approach a constant value and do not coalesce. The N similar to 4P system provides better stabilization because of its broader interfacial width. For N similar to P, hole velocity decreases as phi increases and then becomes constant for phi > 0.03. Relative to blends, holes grow faster in bilayers and eventually coalesce. AFM analysis shows that the PS hole floor is smooth whereas the blend floor contains patches. The film stabilizing effect of block copolymers can be attributed to a decrease in capillary driving force, entanglements at the matrix/copolymer interface, and brush grafting density.