The human neck curves slightly forward (to sustain the weight of the head when upright), and its important to maintain this curve when in a resting position. If the height of the pillow is too high when sleeping sideways or on the back, the neck is bent abnormally forward or to the side, causing muscle strain on the back of the neck and shoulders. This type of position may also cause narrowing of the air pipe, resulting in obstructed breathing, and sometimes snoring, which can hinder sleep. Conversely, if the height of the pillow is too low, the neck muscles can also be strained.
Based on the bodys measurements and personal preference, the pillow should maintain a height of 4 to 6 inches, properly supporting the head and neck (and shoulders when lying on back).
A large part of what makes a good pillow is personal preference. If the pillow feels comfortable, its likely to help one relax, get a good nights sleep, and feel well rested in the morning. The pillow's surface can also be a source of comfort - some people prefer a pillowcase with a cool, smooth feeling (such as a poly/cotton), some prefer warmth (such as terry, flannel or a mix), etc.
