Experiments with captive bats need a flight room that is acoustically neutral, especially when recording and analysing bat calls or the response of bats to certain sound stimuli. Our aim was to identify an isolation material with the best quality–price relationship to acoustically coat such a flight room. For this, we built a flight room divided into two compartments that were to be acoustically isolated from one another. Audible and infrasonic waves are difficult to attenuate with low-cost materials but the attenuation of ultrasounds is rather straightforward. We evaluated the absorbing capacities of different low-cost materials – felt fabric, polystyrene, egg boxes, egg boxes coated with felt fabric, absorbing pyramidal foams, polyurethane foams and cork. The material that showed the best quality–price relationship was the polyurethane foam of open cells (5 cm thickness), which was able to attenuate approximately 20 dB at ultrasonic frequencies.