The simple answer is: it depends entirely on the material. True all-weather furniture made from teak, powder-coated aluminum, synthetic wicker (HDPE), or certain plastics can generally handle rain. However, even these benefit from covers for long-term beauty. For furniture made of steel (unless stainless), untreated wood, iron, or standard cushions, leaving it exposed to rain leads to rust, rot, mold, and fabric damage.
For lasting durability, consider these points. First, know your material. All-weather resins and metals are low-maintenance, while teak grays naturally but remains sturdy. Second, use high-quality, breathable furniture covers. They shield from UV rays and rain while preventing moisture trap, which causes mildew. Third, for wood or metal furniture, apply protective sealants or paints annually. Finally, store cushions in a dry place or use quick-dry, all-weather cushion fills.
In short, you can leave suitable all-weather furniture in occasional rain, but for longevity and appearance, investing in proper covers and routine maintenance is always recommended. This practice prevents costly replacements and keeps your outdoor space ready for enjoyment.