We study how heterogeneity in capital inputs affects firm performance. Drawing on detailed data on municipal bus fleets in Poland, we exploit plausibly exogenous variation generated by public procurement and nationally coordinated sales behavior of bus manufacturers to identify the causal effects of variety in fleet composition across brands and other technical dimensions. More heterogeneous fleets exhibit lower vehicle utilization and, for a fixed level of output, require more units of capital and generate higher costs. Our results emphasize that the productive capacity of capital depends on its internal structure, not only on its aggregate quantity or value.
