Fuselage construction was identical to the earlier Mosquito: a balsa wood "pith" sandwiched between plywood sheets which were laid in diagonal panels. Aerolite formaldehyde cement was the bonding agent. The fuselage halves were built on large concrete or wood patterns and equipment was fitted in each half; they were then joined along the top and bottom centre lines using wooden reinforcing strips. The entire fuselage was then tightly wrapped in fine aviation fabric which was doped in place. The tailfin which had the trademark gracefully-curved de Havilland shape, was an integral part of the rear fuselage. On late F.1s and further models of production aircraft, a fin fillet was added to the base of the unit. The horizontal tail unit was an all-metal structure, again featuring the distinctive de Havilland shape, which was later repeated on the Chipmunk and Beaver.