Martex 300-Thread-Count King Flat Sheet, White 60% cotton The blend of 60% cotton and 40% polyester assures the traditional comfort of cotton and the easy-care characteristics of polyester. Premium-pocket fitted sheets for mattresses up to 18-Inches deep Available in burgundy, eucalyptus, goldenrod, heather, navy, parchment, silver blue and white Offered in twin, full, queen and king sizes and standard pillowcases.