A sliding seismic isolator includes a first plate attached to a building support, and at least one elongate element extending from the first plate. The seismic isolator also includes a second plate. The first and second plates are capable of moving relative to one another along a horizontal plane. The seismic isolator also includes a lower support member attached to the second plate, with a biasing arrangement positioned within the lower support member. The elongate element(s) extend from the first plate at least partially into the lower support member, and movement of the elongate element(s) is influenced or controlled by the biasing arrangement. The seismic isolator also includes a damping structure with closed ends spaced apart from the first plate and the base of the seismic isolator. The damping structure is configured to contain a substance, such as a liquid, gas, silicone, and/or a combination thereof, and to expand longitudinally when it is compressed.