A helmet, comprising: inner and outer shells (3, 2) configured to slide relative to each other; and a connector connecting the inner and outer shells (3, 2) so as to allow the inner and the outer shells (3, 2) to slide relative to each other, the connector comprising: an attachment part attached to one of the inner shell and the outer shell; characterised in that: the attachment part comprises one or more protrusions extending into the inner or outer shell (3, 2) attached to the attachment part, perpendicularly to a radial direction of the helmet, and the inner or outer shell (2, 3) attached to the attachment part comprises one or more channels into which the protrusions extend, the protrusions and channels are configured such that the protrusions can move within the channels in an extension direction of the protrusions, perpendicularly to a radial direction of the helmet, during sliding of the inner and outer shells (3, 2) relative to each other, and characterised in that the protrusions comprise an abutment member configured to abut an abutment portion of the channel to prevent the protrusion leaving the channel when the protrusions move perpendicularly to a radial direction of the helmet. inner and outer shells (3, 2) configured to slide relative to each other; and a connector connecting the inner and outer shells (3, 2) so as to allow the inner and the outer shells (3, 2) to slide relative to each other, the connector comprising: an attachment part attached to one of the inner shell and the outer shell; characterised in that: the attachment part comprises one or more protrusions extending into the inner or outer shell (3, 2) attached to the attachment part, perpendicularly to a radial direction of the helmet, and the inner or outer shell (2, 3) attached to the attachment part comprises one or more channels into which the protrusions extend, the protrusions and channels are configured such that the protrusions can move within the channels in an extension direction of the protrusions, perpendicularly to a radial direction of the helmet, during sliding of the inner and outer shells (3, 2) relative to each other, and characterised in that the protrusions comprise an abutment member configured to abut an abutment portion of the channel to prevent the protrusion leaving the channel when the protrusions move perpendicularly to a radial direction of the helmet. the attachment part comprises one or more protrusions extending into the inner or outer shell (3, 2) attached to the attachment part, perpendicularly to a radial direction of the helmet, and the inner or outer shell (2, 3) attached to the attachment part comprises one or more channels into which the protrusions extend, the protrusions and channels are configured such that the protrusions can move within the channels in an extension direction of the protrusions, perpendicularly to a radial direction of the helmet, during sliding of the inner and outer shells (3, 2) relative to each other, and characterised in that the protrusions comprise an abutment member configured to abut an abutment portion of the channel to prevent the protrusion leaving the channel when the protrusions move perpendicularly to a radial direction of the helmet.