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Your patio cushions have gone flat in the middle, and now you’re deciding what goes back inside the covers. The choice is really between two fills — foam and polyfill — and they fail in opposite ways. Foam keeps its shape for years but holds water. Polyfill sheds water fast but slowly goes flat. Which one lasts longer outside comes down to which cushion you’re refilling.
What you’re actually choosing
The fill is the inside of the cushion. The cover is the outside. People blame the cover when a cushion goes flat, but the cover only keeps rain and sun off the fill — it’s the fill that decides whether the cushion still feels like a cushion after a season of sitting on it in the rain.
Foam is a solid slab, cut to the size of the cushion. Polyfill is loose polyester fiber, the same kind of fluffy stuffing inside a pillow, either loose in a bag or sewn into a finished insert. They sit differently, dry differently, and wear out differently.
Foam, honestly
Foam’s strength is shape. A foam slab holds its edges, supports your weight without bottoming out, and still looks like a rectangle after a full summer. That is why seat cushions — the ones you actually sit on — are almost always foam.
The trade-off is water. Standard polyurethane foam soaks up rain like a sponge and dries slowly, which is how a cushion ends up heavy, musty, and mildewed by August. Outdoor-rated foam is different: reticulated or quick-dry foam is made with an open cell structure that lets water drain straight through instead of sitting inside it. If you’re buying foam for cushions that live outside, that distinction matters more than the brand — indoor foam belongs indoors, even on a covered porch.
Foam is also heavier than polyfill, especially when wet, and it costs more up front. What you get for that is a seat cushion that still feels like a seat cushion in year three.
Polyfill, honestly
Polyfill’s strength is softness and drying. Loose polyester fiber doesn’t absorb water the way foam does, so a polyfill cushion dries out fast after a storm, and it feels softer and more relaxed to sit against — more pillow than platform.
The trade-off is flattening. Fiber compresses a little every time someone sits on it, and unlike foam it doesn’t spring all the way back. A polyfill seat cushion gradually goes thin in the middle, and the only fix is fluffing it by hand or adding more fill. It also shifts inside the cover over time, so one corner ends up fuller than the other.
That makes polyfill the better fill for throw pillows and back cushions — the ones you lean on, not the ones you sit on — and the weaker choice for a seat cushion that takes your full weight every day.
Foam vs polyfill at a glance
| Trait | Foam | Polyfill |
|---|---|---|
| Shape over a season | Holds its shape and edges | Flattens and shifts with use |
| Drying after rain | Slow, unless outdoor-rated quick-dry foam | Fast — fiber sheds water |
| Weight when wet | Heavy — a soaked slab is hard to move | Light — easy to carry inside |
| Comfort | Firm, supportive sit | Soft, relaxed feel |
| Best for | Seat cushions | Throw pillows and back cushions |
| Upkeep | Almost none — just keep it dry | Regular fluffing, top up fill as it packs down |
The covers matter as much as the fill
Neither fill survives a bad cover. A water-resistant cover with a zipper — solution-dyed acrylic or olefin, not cotton — keeps most rain off the fill in the first place, and it matters more for foam than for polyfill, because foam is the one that stays wet. Check that the cover actually fits the fill: a foam slab in a loose cover slides around, and a polyfill insert in a tight cover goes lumpy.
Two habits stretch either fill. Store cushions upright or under cover during a long stretch of rain rather than flat on the furniture, so water runs off instead of pooling. And bring them in for winter — freeze-thaw cycles are what finish off a foam slab that looked fine in October. Our winter cushion storage guide covers the full routine.
Which one to buy
Foam is usually bought as a slab you cut to fit, and polyfill is usually bought as a finished insert. That difference is part of the decision: foam takes a measuring tape and a bread knife; polyfill takes a zipper.
FoamRush Custom Cut-to-Size Foam is the foam pick. It is high-density upholstery foam — 1.8 density with a 44-pound compression rating and full recovery — cut to whatever size your seat cushions need, and the listing calls out outdoor cushion inserts as a use. Measure the inside of your cover, order the slab a touch larger than the cover so it fills the corners, and trim it to fit.
FoamRush Custom Cut-to-Size Foam
High-density foam cut to your cushion’s exact size, firm enough to hold its shape through a full season of sitting.
CASAJOY Outdoor Pillow Inserts are the polyfill pick — a pack of four 12-by-20-inch inserts with a water-resistant cover and 7D hollow polyester fiberfill made from recycled materials. They are throw-pillow inserts, sized for lumbar and accent pillows rather than seat cushions, which is exactly where polyfill belongs. Buy them a little larger than the pillow cover so they fill it out, and expect to fluff them after a hard rain.
CASAJOY Outdoor Pillow Inserts, Pack of 4
Water-resistant polyfill inserts that dry fast and stay soft — the right fill for pillows you lean on, not sit on.
Bottom line
There isn’t one winner — there’s a right fill for each cushion. Refilling seat cushions, buy foam, and make it outdoor-rated quick-dry foam so a storm doesn’t leave you with a soaked slab. Refilling throw pillows, buy polyfill, and accept the fluffing as the price of a soft pillow that dries by morning. And whichever fill you pick, put it in a water-resistant cover — the cover does more for the cushion’s life than the fill ever will.
