Many people try to use Indentation Load Deflection, commonly known as ILD, as a metric when trying to decide which mattress to buy. We are happy to share our ILD data with you, but we also caution you not to base your decision on that number alone. ILD is only accurate when comparing the same type of latex from the same latex manufacturer. We know it would be easier if there was one unified number, but feel is ultimately subjective and based on more than a single input test like ILD. So, please use caution when basing a decision on these numbers.
Now, let's take a deep dive into the world of latex.
"100%" Natural Organic Latex
Our latex adheres to the Global Organic Latex Standard (GOLS) and is classified as "100%" natural. Latex foam is a manufactured product that does not appear in nature. 95% of the material in Spindle’s latex comes out of a tree. The other 5% are ingredients — zinc oxide, fatty acid soaps, sulfur, and sodium — needed to “cure” the raw sap, i.e. so the rubber can be aerated and vulcanized (baked) and made into foam rubber. We think it’s one of the most natural products you can sleep on. No fillers. No synthetic rubber.
Where does latex come from? Latex foam is made from the sap of the rubber tree, hevea brasiliensis, originally native to the Amazon rainforest. Because of rubber’s versatility and wide use, the crop has been industrialized and now grows on sustainable plantations in Equatorial regions around the world.
At 7 years, a rubber tree is considered mature and ready for harvesting. They have a life span of about 32 years, and most trees will produce sap for about 25 years. The harvesting lifespan is longer than the time needed to reach maturity, making the rubber tree crop ecologically sustainable. USDA and/or Forest Stewardship Council guidelines ensure a healthy forest with the ability to satisfy production. Once a rubber tree is retired, it is used for furniture production or burned as fuel.
Harvesting Latex The latex sap is found close to the surface of the tree, an is harvested by cutting shallow slices into the bark. This discharges the sap, which then flows into a container for collection. The slicing of the tree is carefully managed. Varying where the cuts are made allows the shallow openings to heal quickly without doing permanent damage to the tree, nurturing it through its 25 year cycle.
An interesting fact: the latex contained in one Queen sized mattress is made from one day’s production of 2500 trees spread over 12 acres of land.
What are the methods for making natural latex for a mattress? There are two widely used production methods for manufacturing latex foam cores: Dunlop, and Talalay. Both methods deliver long-lasting support and the ability to conform to the body. Dunlop is denser, or more staid. Talalay has a bouncier feel. We’ll get into mattress feel in a bit, but first let’s take a look at the geeky stuff.
Dunlop and Talalay both follow similar manufacturing steps: sap collection, mixing, spreading, cooking, curing, washing, drying, and cutting. The Talalay process adds two steps to the manufacturing (vacuum sealing and flash-freezing).
Neither of the methods is of a superior quality to the other. Both foams are hypoallergenic and resistant to dust mites. We would expect both to be as durable and as comfortable. “Which one” comes down to personal preference, availability, power of suggestion, and price.
Dunlop - History + How it's made? In 1929, Dunlop Rubber chemical researcher Eric Owen developed a process to turn the company’s tire rubber into foam. The Dunlop process describes the first manufacturing method of turning liquid rubber tree sap into latex foam rubber.
When the sap is collected, it is still a liquid. In order to transform it into foam, it is mixed with a small amount (5% of total mixture) of curing agents, mostly fatty acid soaps, zinc oxide, sulfur, sodium and some other compounds. This “curing packet” enables the latex sap to properly foam, vulcanize (cook) and cure. Without curing, the polymers in the latex rubber are able to move independently of each other. In this state, the latex acts more like gum. It gets sticky and loses shape with heat; becomes brittle with cold. It doesn’t have elastic properties like foam rubber. Vulcanization and curing aligns the polymers in the rubber so they act as a unit, and stabilizes the final product. In this state, vulcanized and cured rubber is elastic, conforms to pressure, but then returns to its original shape. Because there are so few latex manufacturers in the world, and because latex is a commodity product, manufacturers need to do something to differentiate themselves. Hence, curing mixture are proprietary (secret) from manufacturer to manufacturer, but the essential components are the same. They may vary slightly in proportion but overall the mixtures are very close to one another. This mixture of latex and curing compounds is thoroughly whipped to properly aerate the foam, and then is poured into large molds to create the Molded Dunlop latex foam cores. The molds are like huge waffle irons, but instead of squares, there are metal pins attached to the top and bottom parts of the mold, to create air holes in the final latex core. The pins are not only used to make holes, but they help with temperature transfer, heating and cooling the foam as it is manufactured. After mixing in big tanks, the foamed latex is spread across the entire bottom of the mold. The top of the mold comes down to join the bottom, and the molded latex is cooked or “vulcanized” by steam heated to 220 ̊F. The vulcanization process takes about half an hour. Then the top mold is released and lifted, the latex foam cores are removed from the bottom mold and placed on a conveyor belt. They travel to a washing system that washes the latex thoroughly with fresh water to remove any residual soaps or curing agents. Without proper washing the cores will soften and sag a great deal more than is desirable; that’s why so much emphasis is placed on washing. Once clean, the cores are then run through a press to remove excess water and thoroughly dried by hot air (think car wash). When dry, the latex foam is cut to size and put through a series of tests to make sure product standards are met. This is standard procedure for the industry. An inconvenient truth: All mattresses will soften, which can sometimes be interpreted as sag. You should anticipate a latex mattress will soften about 15% over a 10 year period. Compare that to the 30-60% sagging with an innerspring or memory foam mattress.
How does Molded Dunlop “feel”? Denser than Talalay, Dunlop has been around the longest. It is the least expensive to produce, and is known for its durability, performance, and ability to reduce motion transfer (a very desirable characteristic when you sleep with a restless partner). Dunlop is produced overseas, mostly in Sri Lanka, India, Malaysia and Vietnam, and is the only latex foam that can be GOLS certified. A variant, continuous pour Dunlop is made by two companies in the US. During the Dunlop vulcanization (steam oven) process, heavier particles of the mixture gravitate to form a layer along the bottom of the mold, producing a latex core that is slightly denser on the bottom and lighter on the top. For most people, this difference between feel of top and bottom is negligible, if able to be discerned at all. In terms of quality and durability, Molded Dunlop stands the test of time. It performs consistently well and has an excellent track record when it comes to not softening or sagging compared to other mattresses. But remember, over time all mattresses will soften up and sag a bit. One tip is to avoid latex made with any fillers. Properly supporting your latex mattress also has a huge effect on longevity. I discuss this in greater detail below.
Talalay - History + How it's made? Developed in the mid-1940s, the Talalay process is similar to Dunlop…up until the part where the foam gets put into the mold. Talalay only pours its latex in two sizes: Queen and Twin XL. Often their latex is seamed (two pieces glued together) but this is not a negative – it actually has no bearing on performance and durability. The only US Talalay manufacturer is based in Shelton, CT, although Talalay latex is also made in the Netherlands and China. With Talalay, computers set the amount of latex to be distributed and it is manually piped in and spread into pin-core aluminum molds. The foam does not cover the entire mold, there is room at the edges for the foam to spread when the mold is vacuum-sealed. The vacuum spreads the foam to the edges of the mold, creating a unique aerated cell structure (think air bubbles) within the latex. After vacuum sealing, the entire mold is flash frozen to -20 ̊F, which sets the air pockets in place and prevents any particles from settling to the bottom. This freezing method gives Talalay foam a bounciness that distinguishes it from molded Dunlop. The aeration of the foam is more uniform from top to bottom within Talalay latex, although there may be variations in density across an entire sheet of Talalay latex. After flash freezing, carbon dioxide is introduced to cause the foam to “gel”. The molds are then vulcanized by steam heated to a temperature of 220 ̊F to cure the latex foam. After it has been cured, the mold opens and the sheets of latex are placed onto a conveyor belt, where they are taken to the washing station. Talalay washes the cores five times with fresh water, and then dries them thoroughly before cutting and storing them.
How does Talalay “feel”? Talalay latex foam is a lighter, bouncier foam than Molded Dunlop. It is springy, and known for its airy feel. It is often used as a top layer on a mattress to offer a more bouncy feel. In actuality, Talalay can be quite firm, like Dunlop, but as a cost savings many companies will layer Talalay over Dunlop. With all things mattress related, personal density or bounciness preference is neither good nor bad, it just is. Whatever you like is what you like!