What is fill weight? Rebecca Leonard April 09, 2019 11:03 Updated Follow Fill weight is simply the weight of the fill inside a pillow. If weight is referred to as "gsm", then it refers to the weight of the fill within a square metre. Shop all our pillows. Related articles What is fill power? What is the benefit of a Down pillow? What is the benefit of a Hollowfibre pillow? Which pillow filling is best for sweating/warm Sleepers? Which pillow fillings are anti-allergenic? Comments 0 comments Please sign in to leave a comment.