The short answer is: it's not recommended. While some cushions are marketed as weather-resistant, prolonged exposure to rain can cause damage. Water can lead to mold, mildew, and deterioration of the cushion's filling and fabric. Even "quick-dry" foams can retain moisture internally, leading to unpleasant odors and a shortened lifespan.
For true peace of mind, the best practice is to bring cushions indoors or into a dry storage area when not in use, especially during extended wet weather. If that's not always feasible, invest in high-quality, specifically waterproof covers designed for your furniture. Look for cushions made with solution-dyed acrylic fabrics and quick-drainage foams for better resilience. Ultimately, proactive protection from rain will significantly extend the life and appearance of your urban outdoor cushions.