This is a 3-Chamber pillow. The center chamber is filled with duck feather, which provides great, resilient support. The feather core makes up about 90% of the total fill weight. The outer chambers are filled with 550 loft duck down, which adds some softness and luxury to the pillow. Down Perfect(TM) pillows combine the firmness of feather with the softness of down for the best of both worlds! The outer shell of this pillow is crisp 255 thread count cotton. The Medium weight is a real crowd-pleaser, and works for front, back and side sleepers. It is firm enough for side sleeping but not so hefty that it props the head up too much for front and back sleeping. If you sleep only/primarily on your side or like a really firm and substantive pillow, go with the Firm version! Note that King size pillows are more sinky than Standard or Queen, as they are quite long. There's more room for the fill to spread out to the sides when laid on. 3 Chamber Pillow in a Pillow Design:Offers the luxury of a down pillow with the support of a feather pillow Outer Shell - 255 Thread Count:Prevents Feather & Down from escaping Outer Shell - 100% Cotton:Fine cotton allows the feather & down to breathe Core Chamber - Nylon:Contains the feather at the center of the pillow.