Decorative pillows serve a dual purpose. They often have fancy cover material which serves to decorate the room where they are found. Since decorative textiles are commonly 54 inches in width, many decorative pillows finish about 17x17 inches. (54/3 = 18 less seam allowance) When used to decorate a fully made up bed, decorative pillows are likely thrown aside at bedtime, since they are not covered with a washable pillow case, thus, while found on the bed, they are primarily there for decoration, hence they fall under this category. These pillows may be custom made, as well as made by freelancers.
Decorative pillows are also found on furnishings in more public parts of the home, such as sofas, chairs and window seats. Here, their common use may overlap both orthopedic and bed pillows. For example, unless a person has some particular medical condition, they will likely use a handy decorative pillow for lumbar support, as needed, while seated on a sofa. Likewise, for the occasional nap, decorative pillows are handy for supporting the head or neck, even though they may not be covered with a pillow case, as are bed pillows.