Using indoor cushions on outdoor furniture is generally not recommended and can lead to several problems. Indoor cushions are typically made from materials like cotton, silk, or standard foam that are not designed to withstand outdoor conditions. When exposed to rain, they will absorb moisture, leading to mold, mildew, and unpleasant odors. Sunlight will cause the fabrics to fade and degrade rapidly, while the filling may break down. Furthermore, indoor cushions lack the protective treatments that repel water, resist UV rays, and inhibit mold growth found in outdoor-specific cushions.
For durability and comfort, invest in cushions specifically designed for outdoor use. These are made with quick-drying, solution-dyed acrylic fabrics, UV-resistant threads, and high-resiliency foam that won't hold moisture. To protect your investment, always use cushions intended for the environment they will occupy and store them properly during harsh weather or off-seasons.