As with mattresses, there is no universal rule here. The choice depends on each person’s specific requirements.
A thicker pillow is generally recommended for those who tend to sleep on their side. This is because it fills the hollow space between the neck, shoulder and mattress. A thinner pillow is better for someone who generally sleeps on their back as it fills the space between the back of the head and the neck, reducing and preventing muscle tension. It is not advisable to sleep face down as the neck is stretched and twisted in this position.