A sofa is a fundamental piece of upholstered furniture designed primarily for comfortable seating of multiple people, serving as the social nucleus of living rooms, dens, and other gathering spaces. Its core structure begins with a frame, traditionally crafted from kiln-dried hardwood (like oak or maple) for durability and resistance to warping, though engineered wood or metal may also be used. Within this frame lies the suspension system, which provides foundational support; common types include eight-way hand-tied springs (premium, offering superior resilience and contouring), sinuous “S” springs (durable and supportive), or elastic webbing (a cost-effective option). Resting atop the suspension is the cushioning system, typically comprising a core of high-density foam, down feathers, polyester fiberfill, or a blend (e.g., foam-wrapped down for softness over support).