I love lounging on the patio in summer when I’m not working, (which seems to be all the time between actual work and three kids).

So when I do get time to kick back and relax on the outdoor furniture, I need to know the cushions will be comfortable and not all squashed down and flat. And this depends on the quality and density of the foam inside.

Outdoor cushions are filled with open or closed cell Polyurethane foam. Open cell foam is medium-hard and does well in dryer climates, and is a good year-round choice. Closed cell foam lasts longer in very wet climates but it tends to be very firm. Open cell foam is more comfortable and expensive.

Let’s dive down into this subject in more detail and look at the history of foam, the makeup of foam – and consider the differences between various types of foam.

What is The Best Foam For Outdoor Cushions?

We are all eagerly awaiting quality patio time. For quality patio time, one of the essentials is comfortable seating. That means comfortable cushions.

Outdoor cushions are designed for our backs and our – posteriors. Back cushions and outdoor pillows are usually softer than seat cushions. Back cushions and pillows are made from compressed polyester batting or polyester fiberfill. Seat cushions need to be stronger. They are usually made of foam. 

So, what’s the best foam for outdoor cushions? It depends on your comfort and your climate.

Polyurethane foam is a medium hard choice that performs well in dry climates but not wet ones. Closed cell foam will last a long time and be an excellent choice in very wet climates – but it tends to be firm. 

Open cell foam is softer and is a good year-round choice. Not surprisingly, open cell foam cushions carry the highest price tag.

A Brief History of Foam

What is foam? Foam is a material (solid or liquid) that has pockets of gas trapped inside. Beer foam is a (delicious) type of liquid foam. Your kitchen sponge is a good example of solid foam. 

Foam is everywhere and it’s been around for a long time. Originally, foam was made from rubber tree sap. The Aztecs and Mayans used foam back in 500 B.C.

Memory foam was developed by NASA – but not for astronauts to sleep on. They developed memory foam for the seat cushions, so the astronauts were cushioned from high-G forces and possible crash landings. 

Open & Closed Cell Solid Foam (Perfect For Outdoor Cushions)

Outdoor cushion foams are solid foams. Solid foams come in two types: open cell and closed cell. A cell is a hole or a pore.

A foam is classified as open cell if more than half its cells are open. Open cell foams are flexible, springy and soft. 

Open cell foam is designed to let water travel right through. It’s not like a sponge. A sponge soaks up water and keeps a lot of it, until you squeeze it out.

Open cell foam is designed with holes that don’t soak up water. The open spaces in this foam all connect like tiny highways. The tiny highways let water run straight through the cushion and out the bottom. 

The open cell structure is made by introducing an inflating agent, like sodium bicarbonate (or baking soda), to the liquid compound during foam production. Open cell foams can be made of polyurethane, PVC, or EPDM rubber. 

Open cell foam cushions are softer and more expensive, but they can be used all year round. Many are treated at the factory with a mold and mildew spray, and you may have to renew the application yearly if you live in a wet area. Because a lot of the foam is open hole space, open cell cushions dry quickly. 

Closed cell foam is sturdier and stiffer. Closed cell foam is used in outdoor cushions, camping mats, insulation, and seals. This foam is firmest because the foam is designed to be proportionately more solids than open holes. 

In closed cell foam, all the open spaces are closed off from each other. No highways – just dead ends. Closed cell foam can be made of polyethylene, neoprene, foam rubber and polyurethane.

Closed cell foam cushions act as moisture barriers. Closed cell foam is very buoyant, and is often used in flotation devices. Closed cell foam has higher compressive strength than open cell foam, so it will hold its shape longer. It is UV resistant.

Polyurethane foam (foam rubber) can be open cell or closed cell. Open cell polyurethane has been used in cushions, mattresses, insulation, electronics and more for decades. This foam comes in different densities and firmness. It is the lowest cost choice.

Polyurethane foam tends to soak up some water and hold it. For this reason, these cushions often come from the factory with an antimicrobial treatment applied. Polyurethane foam cushions may perform better in dry climates.

Here’s a definitive guide to foam.

What Are The Different Densities of Outdoor Cushion Foam?

The more holes the foam has, the lighter weight – and less dense – it is. The higher the density, the higher the durability, weight, resiliency, and – the higher the price tag. 

To measure density, manufacturers cut a one-foot square cube of foam and weigh it. Foam density is measured in pounds per cubic foot. 

Indoor cushions and mattress densities vary from 1.8 (extra soft) to 3.2 (extra firm). Upholsterers use a numbering system to simplify density numbers: a 1.8 cubic foot per pound density becomes #18. A density of 2.4 becomes #24, etc. 

The industry standard for outdoor cushion foam densities run between 1.5 and 1.8 pounds per cubic foot (LB). High density foam cushions have densities of 1.8 pounds per cubic foot or more. 

Here’s a great chart with densities and firmness.

Is High Density Foam Good For Outdoor Cushions?

Yes. High density foam is great for outdoor cushions, either open or closed cell. High density foams, either closed or open cell, will guarantee the best quality. And, they come in a range of comfort choices.

For outdoor cushions, most open cell foam is manufactured as either 1.8 or 2.2 pounds per cubic foot. Open cell foam cushions come in either medium or firm hardness.

Closed cell foam cushions are much denser. They range from 3 and 6 pounds per cubic foot. Closed cell foam cushion hardness ranges between firm and extra firm.

Polyurethane cushions also come in high density. High density polyurethane foam is offered in medium, firm, and extra firm options. 

Is High Density Cushion Foam Waterproof?

While Spring showers may be good for flowers, it leaves our outdoor seating too wet to sit on. Do they make waterproof cushions?

Water-resistant and waterproof are quite different things, although the words are often interchanged. Waterproof means water will bead up and run off – no soaking in, ever. 

Water-resistant means waterproof from the factory, but after some wear it needs help being waterproof. Help comes in the form of spray waterproofing chemicals. There are lots of effective waterproofing sprays on the market.

High density, open cell foam cushions are not waterproof. Water doesn’t run off – it runs straight through them.

High density, closed cell foam cushions are water resistant. Very high density closed cell foam can be waterproof, but the cushions wouldn’t be very comfortable – too hard!

How Can I Make My Outdoor Cushions Firmer & More Comfortable?

If your cushions are too soft for you, try adding some denser foam – like closed cell foam. 

Let’s say you have open cell cushions. You love that rain drains out of them, but they are just too soft. Try buying some thin sheets of firm or extra firm closed cell foam. Cut them to size. Then open the fabric cover and put a firm sheet below the open cell cushion.

If it still isn’t firm enough, use two extra firm sheets, one on top and one on bottom of the soft open cell. Once you have the perfect firmness, modify the closed cell foam so water can run through. 

Try puncturing the closed cell sheets to allow water to travel through. If you’re sure you’ve found your Goldilocks cushion, you can use spray glue to keep the layers together.

How Long Will Outdoor Cushion Foam Last Before it Needs Replacing? 

Experts say that a high density foam cushion (1.8+) will last at least five years and up to 12 years.

Final Thoughts

Outdoor cushions vary in price and level of support depending on how dense and high quality they are. For long-lasting comfort on outdoor couch and chair cushions – it’s therefore always preferable to buy top standard foam.

Like many things in life, choosing poor quality, soft or easily compactable foam is a case of ‘buy cheap, buy twice’ – and could quickly lead to those squashed, flat cushions that nobody wants to park their derriere on. And then where would we all be? 🙂