The short answer is: it's not advisable. While many modern outdoor fabrics are water-resistant, they are not entirely immune to damage from prolonged rain exposure. Leaving upholstered pieces outside during rain can lead to several problems. The cushions can absorb moisture, leading to mold, mildew, and unpleasant odors inside the filling. The fabric itself may fade, stain, or degrade faster. Even if the fabric dries, the underlying foam or padding may stay damp, creating a breeding ground for bacteria.
To protect your furniture, the best practice is to bring cushions and pillows indoors or into a dry storage area when not in use, especially during prolonged wet weather. If that's not possible, invest in high-quality, waterproof furniture covers designed for breathability. For frequent use, choose furniture labeled with "all-weather" or "quick-dry" fabrics and consider frames made from rust-proof aluminum or synthetic wicker. Always shake off excess water and allow cushions to dry completely in the sun before placing them back on the furniture. With proper care, you can significantly extend the life and appearance of your upholstered outdoor pieces.