Pillows insert are made of Soft Microfiber Fabric with 100% Virgin polyester fiberfill. We generally recommend using inserts that are 2" larger all around than your finished pillow size. For example if you have an 18x18 pillow cover, you'll want to use a 20x20 insert. This will ensure that your pillow looks plump and luxurious. If the insert is too small, the pillow cover will look saggy.