When selecting a design sofa, focus on the internal structure and material density. Ensure the frame is made of kiln-dried solid wood (moisture content <12%) or reinforced steel to prevent warping. For comfort and longevity, the seat cushions should feature high-resiliency (HR) foam with a density of at least 35-45kg/m³, ideally topped with down feathers or memory foam for a premium feel. Additionally, verify the Martindale rub count of the upholstery; for commercial or high-traffic residential use, a rating of 30,000+ cycles is essential for durability.