4 Options: 18" x 18" - Fits our 18" Pillow Cover. 20" x 20" - Fits our 20" Pillow Cover. 16" x 26" - Fits Our 16" x 26" Pillow Cover. 26" x 26" - Fits Our 26" x 26" Pillow Cover. Our Down Alternative Pillow Inserts will be your new favorite insert! Soft and fluffy like a down insert with no allergens, cruelty free, and no feathers to poke you. Made with 100% Polyester fiber filling that is silky and the ultimate in softness.