Outdoor (or reticulated, or dry-fast) foam is made with a large open-celled structure that allows water to drain through the foam quickly and easily, allowing it to dry more quickly after it has gotten wet. Traditional indoor foam, also made from petroleum, has a much more closed cell structure, which retains water and takes longer to dry. If your Sunbrella® cushions will be primarily used outdoors where they will be exposed to rain, snow, and moisture from dew, we recommend outdoor foam. If your foam will be used in a screened-in porch, or indoors, then we recommend traditional polyurethane foam. Traditional dacron batting can be used with either of these cushion and foam types, as it drains quickly and tends to allow moisture to pass through easily.