The term 'Pillow Filler' refers to the material used to fill a pillow. The most common materials used are EIDER (5 letters), DOWN (4 letters), FOAM (4 letters) and EIDERDOWN (9 letters). EIDER is a type of duck that produces a soft, lightweight DOWN which is often used as a pillow filler. DOWN is the soft, fluffy feathers found under the tougher exterior feathers of birds such as ducks and geese. FOAM is a synthetic material made from polyurethane or latex that is often used as a pillow filler. EIDERDOWN is a type of DOWN that is harvested from the EIDER duck and is considered to be the highest quality DOWN available for use in pillows.