Continuous positive airway pressure (CPAP) systems for preterm infants work with conventional ventilators or use a jet ventilation system. It is assumed that the most important advantage of jet‐CPAP systems is a lower expiratory resistance (RE). We investigated the RE of seven different CPAP systems. We studied two primary‐care CPAP systems, three jet‐CPAP generators, and two conventional CPAP devices. All devices were adjusted at 6 mbar and connected with a test lung simulating a standardized expiration volume. Maximum pressure increase during expiration was measured and maximum RE was calculated. In primary‐care CPAP devices, the maximum RE of the Benveniste valve was 9.7 mbar/L/s (SD 1.2) while that of the Neopuff was 102.8 mbar/L/s (SD 7.9) (P < 0.01). In jet‐CPAP devices, the RE of the Infant Flow was 6.8 mbar/L/s (SD 1.7), the one of the Medijet REF 1000 was 43.5 mbar/L/s (SD 1.5), and that of the Medijet REF 1010 was 36.7 mbar/L/s (SD 0.3) (P < 0.01). In conventional CPAP systems, the RE of the Baby Flow was 29.7 mbar/L/s (SD 1.1) and that of the Bubble CPAP was 37.1 mbar/L/s (SD 4.3) (P < 0.01). All CPAP devices created an RE. Jet‐CPAP devices did not produce lower RE than conventional CPAP devices.