The general perception of motorists is that motorcycle helmets not only protect riders against head injuries but also isolate them from the outside noise. However, the acoustic insulation of the helmet is not necessarily as effective as it is perceived. To objectively evaluate the acoustic insulation of the helmet, the insertion loss of a sample of five helmets of full face types from different manufacturers was measured in an semi-anechoic chamber. In the whole processa dummy with microphones in the ear (HATS) was used. The measurement was made according to ISO 4869-3:2007, and it studies three directions of sound arrival (front, lateral and rear). The results obtained indicate that the values of insertion loss are negative in the frequency range of 16 to 250- 315 Hz. Furthermore, according to the test, in the range of 250 and 800 Hz there is little insulation, and from 800 Hz insulation increases at a rate of 12 dB/octave or 6 dB/Octave. It has been shown that the occurrence of negative values of insertion loss between the 16 and 250-315 Hz is not attributable to the diffraction of the helmet. Nevertheless, the explanation of this phenomenon may be related to the geometry inside the helmet. The variety of helmets used in this study allows us to extrapolate this result to any helmet of this type. The independence of the insertion loss in relation to the state of the vents (open or closed) has also been demonstrated.