Helmet

A helmet (1) comprises: an outer shell (2); an inner shell (3) lining an inner surface of the outer shell and formed from an energy absorbing material configured to protect against a radial component of an impact to the wearer's head; and a low friction sliding interface (4) between the inner shell and the outer shell configured to facilitate sliding of the inner shell relative to the outer shell in response to an impact to the wearer's head to protect against a tangential component of the impact; wherein the inner shell comprises a plurality of shell segments (30) each shell segment being configured to slide relative to the outer shell at the sliding interface and each shell segment being configured to move relative to each other shell segment.