The matrix is a defining feature of biofilms and supports the formation of structures that enhance access to oxygen in different biofilm models. Using Pseudomonas aeruginosa PA14, Madsen and colleagues (p. 8414 – 8426) evaluated the relevance of matrix production to in-biofilm ecology and evolvability. Pel polysaccharide is a critical matrix component in pellicle (air-liquid interface) and colony (solid-surface) biofilms. Pel production could be exploited by nonproducing mutants (“cheaters”) in colonies but not in pellicles. Pellicles favored spontaneous mutants with enhanced Pel production that were disfavored in colonies. Facultative control of Pel production is therefore advantageous even in biofilm models with similar constraints on oxygen availability.