Using regular indoor pillows on outdoor furniture is not recommended and will likely lead to their ruin. Outdoor environments expose pillows to multiple damaging elements that indoor pillows are not designed to withstand.
Sunlight causes fabrics to fade and weaken, while rain and humidity can lead to mold and mildew growth inside the filling. The pillow's filling material, often down or synthetic fibers, will clump and lose its fluffiness when wet and may never fully recover. Furthermore, outdoor debris and pollen can stain the fabric, and the pillows become targets for insects or other pests.
For temporary use on a covered patio during perfect weather, you might get away with it for a short period. However, for long-term use, you should invest in pillows specifically designed for the outdoors. Outdoor pillows are made from durable, solution-dyed acrylic fabrics that resist fading and are filled with quick-drying materials like polyester foam. They are also often treated to be water-resistant or mold-resistant.
If you must use an indoor pillow outside briefly, always bring it in immediately after use and never leave it exposed to dew overnight. For a lasting and attractive outdoor space, choosing purpose-built outdoor pillows is the only way to ensure your comfort and décor withstand the elements.