This pillow is filled with Ultra fibre, a synthetic substance which has been treated to be anti-microbial and anti-bacterial, so allergy sufferers can have a restful sleep. Ultra fibre is very sturdy and bouncy, and perfect for a high-loft pillow. It is recommended that side sleepers use a high-loft pillow, as you require more support to keep your spine aligned as you sleep. This pillow is also date stamped, so you know when it's time to change, and completely machine washable to help maintain freshness for longer. The cotton cover adds breathability.