The aircraft experienced an inflight structural failure of its upper wing during aerobatics in an air show. The aircraft was landed safely and the pilot was not injured. The upper wing leading edge ribs reportedly collapsed as the pilot began to pull up at the beginning of an eight-sided loop at about 200 knots. An FAA observer reported that about 60% of the upper wing fabric then peeled rearward and separated. The pilot 'aborted the show' and landed without further incident. Examination by an FAA inspector and the owner revealed that the leading edge of the upper wing had collapsed rearward to the front spar with all nose ribs broken. This aircraft is one of two with 'Kermit Weeks' wings. The failure described has also happened with the other aircraft. Both aircraft upper wings had been constructed of lighter weight materials with emphasis on improved performance. Subsequent to this accident the wing was rebuilt with stronger materials to withstand higher loads.