Outdoor cushions can be filled with a variety of materials, depending on the desired look and feel. Some popular fillings include polyester fiberfill, down, and foam. Polyester fiberfill is a synthetic material that is often used in outdoor cushions because it is inexpensive and easy to care for. Down is a natural material that provides good insulation and cushioning, but it can be more expensive than other options. Foam is also a popular choice for outdoor cushions, as it provides good support and durability.