Cushions are sold separately from frames on purpose. The fabric is the part that eventually shows its age, and buying it as its own item means you can refresh the look of an entire patio in a few years without replacing furniture that is still structurally perfect.
Poolside cushions get sat on soaking wet, then baked in direct sun. These use solution dyed outdoor fabric where the colour is locked into the fibre rather than printed on the surface, so it resists fading, chlorine and mildew. The foam is quick drying and open cell, which means water passes through instead of pooling inside and souring.
Cushions are cut to specific frames, so match the product family and the exact model. A Signature Chaise cushion will not fit a Chaise Deep, and a Mainstay dining side chair pad is a different size from the arm chair pad. If your furniture is already installed, check the model name on the underside of the frame before ordering. Store cushions in a deck box or a storage coffee table over winter and they will last considerably longer.