Loft Is the Only Number That Predicts How Long a Cushion Lasts

Fill type is what a cushion is made of. Loft is how long it keeps working. They are different properties, and only one of them tells you anything about what happens in year three.

Two numbers, both comparable, neither optional

Loft is the thickness of a cushion before you sit on it, measured in inches. Manufacturers list it, though not always, and when they do it is the single most useful figure on the page.

Fill power applies only to down and feather — the cubic inches a given weight of down occupies. Higher is better for that weight. It does not apply to foam or polyester at all, so a cushion described with a fill power figure is a down cushion, and a cushion with no fill power figure is not necessarily lacking one.

A third figure appears on some pages and confuses more than it helps: density. Foam density is the weight of a cubic foot of the foam before it is made into a cushion, expressed in pounds. Higher density foam resists breakdown better. It is a manufacturing input, not a comfort measure, and it cannot be judged without knowing how the cushion was cut.

How each filling loses loft

Foam loses it structurally. The open cells break down at their walls and stop returning to shape. This is not fixable, not reversible, and it happens faster in a cushion that carries weight every day than one that sits unused. A high-density foam lasts longer than a low-density foam of identical loft, which is why two cushions with the same thickness can have completely different service lives.

Polyester fibre loses it by matting. The hollow fibres collapse and tangle together into a denser mass. This is why a polyester cushion that feels perfect for a year can feel noticeably thinner by year three, and why fluffing restores some of it initially — the fibre can still be rearranged — but less each time.

Down and feather lose it by cluster breakdown, and this is the recoverable case. Down does not wear out so much as separate: the clusters that hold loft break apart into their constituent fibres. Beating and fluffing redistributes them and recovers much of the height. A down cushion that is fluffed nightly can hold its loft for years; the same cushion untouched will not.

Down-wrapped foam splits the difference. The down surface maintains the visual loft while the foam core holds the shape, so it does not flatten behind a shoulder the way all-foam does. It is heavier and costlier, and the foam core still breaks down on its own schedule.

What loft is actually worth measuring in

For a seat cushion, 4 to 6 inches uncompressed is the common range. Below 3 inches you are looking at a decorative cushion, not something that will support someone sitting down.

For a decorative throw pillow, 3 to 4 inches. These are meant to look full, and the way to fill them is a separate question from their dimensions. Where the cushion goes changes the number entirely — how to size a throw for a sofa covers the measurements that decide it.

For a back cushion, loft matters less than how it attaches. A loose back cushion that compresses simply moves back into place, which is why a down back cushion outlasts a foam one in normal use.

The compression test you can do in a shop

Press firmly into the cushion with the flat of your hand, hold for ten seconds, and release. Then press the two sides toward each other and release.

If the first test recovers most of its height within a few seconds, the filling has structural integrity. If the second test recovers fully, the foam core has not broken down permanently — that failure mode takes years and cannot be tested in a shop. If neither recovers, the cushion is already finished regardless of what the tag says.

How long, honestly

There is no defensible number, and anyone quoting one is extrapolating. What can be said from the mechanism:

• Foam failure is permanent and appears as a slow loss of recovery rather than a sudden collapse
• Polyester mats progressively and never fully recovers once matted
• Down degrades in quality rather than quantity — the loft is there, the loft is not springy
• Density is the only variable that meaningfully changes the foam timeline, and it is rarely published

The honest position is that a cushion’s life depends on two things you cannot measure in a shop: how dense the foam is, and how much weight sits on it daily. Everything else on the page is either a comfort preference or a description of what it is made of.

The mechanical test matters more than any of it. Loft is the one figure on the spec sheet that predicts long-term behaviour, and it is the one most often left off the page. Where it is not stated, that absence is itself worth asking about before you buy — and for what each filling does as it ages, see pillow fill types compared.