The flexible twin-frame construction gives Deuter's award winning Aircomfort Flexlite System its special lightweight properties, excellent ventilationand superb ergonomic fit. The secret lies in the combination of complimentary flexible round and stable flat spring steel frame profiles. The construction easily follows body movements and transfers the load perfectly to the hip fins. It also gives the back mesh a stable tensioned platform for the patented Deuter three-sided ventilation system. For backpacks system. For backpacks with smaller volume they use a round profile frame for full function and flexibility with minimum weight.