To increase the firmness of a soft sofa, one can employ several methods that address either the cushioning material or the underlying support structure. The primary cause of excessive softness or sagging is often the degradation and compression of the internal cushion filling over time. A direct and effective intervention is to modify the cushion inserts themselves. This can be accomplished by replacing the existing filling with a new, higher-density foam core. High-density foam provides superior resistance to compressive forces, thereby creating a much firmer seating surface. For a more refined result, this new foam core can be wrapped in polyester fiberfill or batting, which helps to fill out the cushion cover and add a layer of surface loft.
An alternative or complementary approach focuses on reinforcing the structural support beneath the cushions. If the sofa's springs or webbing have lost their tension, the cushions will not have an adequate foundation, leading to a sinking sensation. To counteract this, a rigid substrate can be introduced between the sofa frame and the seat cushions. A common and economical solution involves cutting a piece of plywood to fit the dimensions of the seating area and placing it directly on top of the frame. This provides a solid, unyielding base that prevents the cushions from sinking into a weakened support system, thereby creating an immediate and noticeable increase in firmness. This method is particularly effective for addressing sag caused by worn structural components rather than compressed cushion filling.
