The Eameses constantly made use of new materials. The pair's first plywood chair — the Eames Lounge Chair Wood (LCW)—made use of a heavy rubber washer glued to the backrest of the chair and screwed to the lumbar support. These washers, which have come to be called 'shock mounts', allow the backrest to flex slightly. This technology was brought back in the 670 Lounge chair. The backrest and headrest are screwed together by a pair of aluminum supports. This unit is suspended on the seat via two connection points in the armrests. The armrests are screwed to shock mounts which are connected only via glue to the interior of the backrest shell, allowing the backrest and headrest to flex when the chair is in use. This is part of the chair's unusual design, as well as its weakest link. The shock mounts have been known to tear free causing catastrophic collapse and damage.