Fully-adjustable head Rest provides personalized neck relief and head support, adjustable lower-back lumbar support allows for free adjustment of both height and depth of support, 4D adjustable armrests can be adapted for different office applications with full 360° rotating handrails, 90°-140° reclining backrest adjustable for multiple work positions, Seat Height can be adjusted for 10cm (3. 9 in.) total vertical travel Ergonomic design recognized by the ergonomics application association for providing ergonomic designs based on extensive research conducted with digital models of the human body. The angles of the backrest have been designed to ensure constant support of back and lumbar. Our products are designed specifically for those who are in an office chair for extended periods of time and require intensive-use seating for comfort. High quality materials the aluminum base is steady and durable while offering excellent resiliency against wear. Silent castors roll, rotate, and move freely without noise. Double-backed-frame design is sturdy and durable. SIHOO is the realization of decades of research conducted by professionals in product design, and mechanical engineering. We do our absolute best to make sure the smallest details are designed with comfort and safety for each customer. Every aspect of our chairs has been assessed with strict safety and quality testing, including but not limited to cushion impact tests, handrail fatigue tests, and chair-frame Static pressure tests, to ensure a product that exceeds expectations. Warranty period is two years. If there are any quality problems, please contact us. After confirming, we will provide a replacement part or product for you. SIHOO provides full parts coverage for the two years of the period, at zero cost for you!