Lotus' innovation with the 88 was a novel twin-chassis layout. The outer chassis supported the aerodynamic elements and the body, and the inner one held the driver, engine, and transmission. The separate pieces allowed the car to meet the rules in the pits, but the outer chassis would create a seal with the track at speed to preserve the ground effect downforce. The organizers decided this ingenious solution went contrary to the rules against side skirts, and they banned the 88.
However, this Lotus was important for a second reason. The inner chassis was F1's first carbon fiber monocoque. The lightweight material is common in racing and performance cars today, but it was a cutting-edge innovation for 1981. Get the full story from Clive Chapman in this clip.