Sensor platforms can benefit from the incorporation of polymerbrushes since brushes can concentrate the analyte near the sensor surface. Brushesthat absorb acetone vapor are of particular interest since acetone is an importantmarker for biological processes. We present a simple procedure to synthesize acetoneresponsivepoly(methyl acrylate) brushes. Using spectroscopic ellipsometry, we showthat these brushes respond within seconds and swell by more than 30% when exposedto acetone vapor. Moreover, quartz crystal microbalance measurements demonstrate that the brushes can be exploited to increasethe acetone detection sensitivity of sensors by more than a factor 6. Surprisingly, we find that the swelling ratio of the brushes inacetone vapor is independent of the grafting density and the degree of polymerization of the polymers in the brush. This isqualitatively different from swelling of the same brushes in liquid environments, where the swelling ratio decreases for increasinggrafting densities. Yet, it indicates that the brushes are robust and reproducible candidates for implementation in vapor sensorsystems.