Journal
Down vs down-alternative: which suits your sleep position
Down is measured in a steel cylinder under a falling plate; down-alternative mostly isn't measured at all. Here's how the two really compare, position by position.
By Sam Winters
Review Editor
Last updated
What does fill power actually measure?
It's a real laboratory number with a real standard behind it: under the International Down and Feather Bureau's method, thirty grams of down is conditioned with steam, rested for days in a climate-controlled room, then measured in a 288-millimetre cylinder under a precisely weighted plate. The volume it holds up is the fill power — reported today as cubic inches per thirty grams.
Two consumer takeaways from the standards world: the traditional 'per ounce' phrasing survives from an older cylinder and the modern unit is per-thirty-grams; and different regions run different systems, so cross-brand numbers only compare cleanly within one method. Testing bodies describe seven hundred and up as extremely high quality under the US approach.
Down-alternative microfibre, by contrast, usually ships with no fill measurement at all — which is exactly the transparency gap we flagged in our pillow review, where the brand publishes neither fill weight nor fill power.
Doesn't synthetic win on allergies?
The research mostly says the opposite of the assumption. New Zealand bedding studies measured around seven times more dust-mite allergen in synthetic pillows than feather ones, and a twelve-month paired study found new synthetic pillows accumulated allergen faster on the same beds. Allergist practice guidance adds that foam pillows are no less mite-prone than feather — its recommendation is mite-proof encasement, whatever the fill.
Genuine down allergy exists, and vegan buyers choose synthetic on principle — both are real reasons. 'Synthetic because mites' largely isn't.
So which fill for which position?
Side sleepers need the most height and steady support — a firmer, higher-loft profile that quality down achieves at high fill powers and down-alternative achieves cheaply with dense microfibre. Back sleepers need moderate, shapeable loft, where down's mouldability shines. Stomach sleepers need low and soft, which argues for a thin down pillow or simply less fill.
Whatever the material, height beats fill in the clinical literature — measure yourself with our loft method before choosing either aisle.