The short answer is: it depends entirely on the cushions' material and construction. For true peace of mind, it is generally recommended to bring standard cushions indoors when it rains or during prolonged bad weather.
Standard polyester or cotton-blend cushions are not designed for constant moisture. Rain can lead to mold, mildew, internal foam rot, and fading. While many modern outdoor fabrics are water-resistant, this means they repel light showers but will eventually soak through in heavy or persistent rain. The trapped moisture is the real enemy.
For a truly low-maintenance solution, invest in all-weather cushions. These are made from quick-dry, waterproof fabrics like solution-dyed acrylic (e.g., Sunbrella) and use quick-drain foam. They are built to withstand sun and rain. However, even these benefit from being stored during harsh storms or for the winter.
Best Practices for Cushion Care:
1. Check Labels: Always follow the manufacturer's care instructions.
2. Use Storage: A deck box or storage bench provides quick, easy shelter for cushions during unexpected rain.
3. Employ Covers: Waterproof furniture covers are a good secondary defense for fixed cushions.
4. Ensure Airflow: Store cushions dry and in a well-ventilated area. Use cushion racks or stands to elevate them off wet surfaces.
5. Clean Regularly: Brush off debris and clean with a mild soap solution to prevent stain setting and mold growth.
In summary, you can leave high-performance all-weather cushions outside with less worry, but bringing any cushions in during heavy rain will significantly extend their lifespan and keep your urban outdoor space looking fresh all season long.