Buying guide
Open-Cell vs Closed-Cell Foam: Which One Belongs in a Cushion?
How open-cell and closed-cell foam differ, what each is used for, and why seat cushions use open-cell foam, including fast-draining reticulated foam for outdoor cushions.
On this page
Updated November 2026 · By Sam K, Fabrica Kraft
Quick answer: Closed-cell foam is made of sealed bubbles, so it is firm, doesn't soak up water and floats. Open-cell foam has connected cells, so air moves through it and it compresses softly when you sit on it. Seat and back cushions use open-cell foam because it is comfortable and breathes. For cushions that get rained on, choose reticulated open-cell foam such as Dry Fast, which lets water drain straight through. Closed-cell foam suits thin pads, flotation and kneeling mats rather than seats.
"Open-cell" and "closed-cell" come up whenever people shop for outdoor or boat cushions. The names describe how the tiny bubbles inside the foam are built, and that structure decides how the foam feels, breathes and handles water.
The difference in one table
| Open-cell foam | Closed-cell foam | |
|---|---|---|
| Cell structure | Cells are connected, so air can pass between them | Each cell is sealed off from the next |
| Feel | Compresses and springs back; comfortable to sit on | Firm and dense; little give |
| Water | Standard open-cell foam soaks water up; reticulated foam lets it drain through | Doesn't absorb water; floats |
| Breathability | Breathes, so it stays cooler to sit on | Doesn't breathe |
| Typical uses | Sofa, chair, bench and outdoor seat cushions, mattresses | Life jackets and flotation, camping and kneeling pads, gaskets, packaging |
| Common materials | Polyurethane foam, including reticulated foam | Polyethylene, EVA and neoprene foams |
What is open-cell foam?
In open-cell foam, the walls between the tiny cells are broken, so the cells link up into a network. When you sit down, air is pushed out; when you stand up, it flows back in and the foam recovers. That is what makes it comfortable for seating, and why almost every sofa, chair and bench cushion is made from open-cell polyurethane foam.
The catch is water. Standard open-cell foam behaves like a sponge: rain soaks in and takes a long time to dry, which is how outdoor cushions end up damp and mildewed. See how to get mold out of outdoor cushions.
Reticulated foam: open-cell foam that drains
Reticulated foam is open-cell foam with the cell walls removed, leaving an open skeleton. Water runs straight through it instead of being held in it, and air dries what is left. That makes it the right foam for patio, pool and boat cushions that get wet. Our Dry Fast foam is reticulated foam, cut to your size. Read which foam outdoor cushions need for more.
What is closed-cell foam?
In closed-cell foam, every bubble is sealed, like a mass of tiny balloons pressed together. Water and air can't move through it, so it floats, resists moisture and stays rigid. Those are useful qualities for flotation, insulation, kneeling pads and protective packaging.
For seating, the same qualities work against it. Closed-cell foam feels hard, doesn't breathe, and gets warm to sit on. It sometimes appears as a thin layer in marine seating or as a camping pad, but rarely as the main foam in a comfortable seat.
Which foam should you choose?
- Indoor sofa, chair and bench cushions: open-cell high density foam. See our foam cut to size.
- Covered porch or patio: high density foam under a Sunbrella cover usually gives the most comfortable seat.
- Cushions left in the rain, by the pool or on a boat: reticulated Dry Fast foam, so water drains instead of soaking in.
- Flotation, kneeling pads or insulation: closed-cell foam, from a specialist supplier. We don't cut closed-cell foam.
Not sure about firmness and thickness? Our cushion thickness and foam guide compares each foam we cut, and Dacron wrap explains how to soften the top of a firm foam.
A note on fabric
Foam is only half the story outdoors. Most Sunbrella upholstery fabric is water-repellent, not waterproof: light rain beads off, but heavy rain can soak through to the foam. The Sunbrella Rain and marine ranges are waterproof. Pair the right fabric with the right foam: see Sunbrella cushions.
Frequently asked questions
Is closed-cell foam good for seat cushions?
Not usually. It is firm and doesn't breathe, so it is uncomfortable for long sitting. Open-cell foam is the standard for seats.
Is open-cell foam waterproof?
No. Standard open-cell foam absorbs water. Reticulated open-cell foam doesn't hold water; it lets it drain through.
What foam is best for outdoor cushions?
Reticulated open-cell foam, such as Dry Fast, for cushions that get wet. Under cover, high density foam is often more comfortable.
Is Dry Fast foam open-cell or closed-cell?
Open-cell. It is reticulated, so water drains through it rather than being trapped.
Which foam floats?
Closed-cell foam floats because its sealed cells hold air and keep water out.
