Process:Continuous Pour Dunlop
Type:"100%" Natural Latex [Commonly Called]
Manufactured: Pennsylvania, USA by Mountain Top Foam
ILD + Density
Lets talk about latex. Fasten your seatbelt. We're about to go into a deep dive into the world of latex mattresses.
A good place to begin a discussion about latex is with the materials we use. It's called "100% natural". It does not contain synthetic latex, fillers, polyurethane or other petroleum based products and differs only slightly from that which carries a certified organic label. Our foam is manufactured by Mountain Top Foam in Mountain Top, PA. Guatemala is the primary source for raw latex. As needed they will also import raw latex from India, Malaysia, Thailand, Indonesia, and Sri Lanka.
Latex is the white milky sap that comes from the rubber tree. Rubber trees were only indigenous to the Amazon rain forest so it can only be grown in regions with similar climate therefore the growing regions are restricted to 15 to 20 degrees latitude north or south of the equator.
In its raw natural state, i.e.: when it's tapped from the tree, latex is a colloid, a liquid that's not conducive to being used in a mattress. “Natural” refers to the source of the latex. 95% of the stuff inside your mattress comes out of a tree. The remaining 5% is comprised of materials needed to aerate [foam] and vulcanize [bake] the latex [liquid]. These processing solutions typically include a mixture of zinc oxide, fatty acid soaps, sulfur, sodium and other ingredients. The curing package is considered "proprietary" in nature, in that each manufacturer uses minor variations in the proportions of the ingredients within this 5% of materials, which may produce slight differences in feel. One analogy would be we both use the same ingredients to make a chocolate cake, but mine has more cocoa powder, while yours has a little more sugar. We both use cocoa powder and sugar, just in slightly different proportions. Once the foam is cured and vulcanized, it is washed a minimum of three times to remove any proteins and other residuals that may be left over after curing.
Our latex is what is referred to as 100% natural. Latex is only natural in a liquid state. Liquid latex is the tapped sap of the hevea brasiliensis rubber tree, much like maple sap is tapped from a maple tree. The finished/manufactured foam rubber we use is natural liquid latex mixed with a proprietary formula of zinc oxide, fatty acid soaps, sulfur, sodium and other compounds that are essential for the vulcanization, foaming, and curing process. This added formula is the only way to turn the pure liquid into foam. All 100% natural latex is made this way — 95% of the final foam is pure liquid latex, while 5% of the final latex foam is the curing package. The curing package is made of the same ingredients across the board, but what varies are the exact proportions of each ingredient from manufacturer to manufacturer.
After it is cooked (vulcanized) the finished natural latex foam core is then washed a minimum of three times to remove all residuals and proteins that may be left over after curing. In the end, it is the most pure, natural latex available; free of any man made synthetic latex. Please note that all “100% Natural Latex” on the market is made this way. Even certified organic latex is produced in this fashion.
The raw liquid latex is sourced globally because the hevea brasiliensis, rubber tree, is not found in the US. It is typically brought in from Guatemala and occasionally from India. The latex is certified to Oeko-Tex 100 – Class I, which is the most stringent standard. The certificate can be verified by entering the certification number 16.HUS.00338 on the Oeko-Tex website.
As mattress makers we question the value the Organic moniker brings to latex foam other than "feel good". Using cradle to cradle or carbon footprint metrics it's not unreasonable to argue that synthetic latex is Greener. We have made a considered decision to stick with Natural latex for now. You can learn more about the organic standards on the Control Union's site, who developed and administer the GOLS.
Our latex is certified to Oeko-Tex 100 – Class I, which is the most stringent standard. The certification number is 16.HUS.00338. And, you may check to ensure the certification is valid on the Oeko-Tex website.
Though it meets the highest standards for its category we're remain careful about the claims we make: what gives me the heebie-jeebies won't affect you at all. Ask what metrics are being used when a mattress promises to be non-toxic, hypoallergenic, 100% natural; that you'll sleep through the night or wakeup pain-free. Or why does something advertised as an Organic Latex mattress change once you read the fine print.
Latex foam rubber is made from the sap of the rubber tree, hevea brasiliensis. Originally found in the Amazon rainforest of South America, today most plantations are located in Asia Pacific (Sri Lanka, Indonesia, Malaysia) West Africa, and Central and South America (Guatemala). On plantations, rubber trees have a life span of about 32 years. At 7 years, a rubber tree is considered mature and ready for harvesting. Most trees will produce sap for about 25 years and then be used as wood for furniture or burned as fuel. Because the harvesting lifespan is longer than it takes for a tree to reach maturity, rubber trees are ecologically sustainable. It is possible to continually renew the rubber tree forest as a usable source without depleting the forest or plantation.
There are three production methods used to make latex foam cores: Molded Dunlop, Talalay, and Dunlop Continuous Pour. (Both molded Dunlop and Talalay use molds for their latex, while Dunlop Continuous Pour has developed a manufacturing line that does not require individual molds.) All manufacturing methods create a product with more similarities than differences. Across the board, latex is known for its elasticity and durability. It has a long-lasting ability to conform to and support the body. While all mattresses do soften and sag, latex mattresses do so at half the rate of a regular innerspring mattress! Over time, you might see 30-60% softening and sagging with an innerspring mattress, while the rate for a latex mattress is only 15%.
All manufacturing methods follow similar steps: sap collection, mixing, spreading, cooking, curing, washing, drying, and cutting. The differences lie more in the feel of the end result. Molded Dunlop latex is known to be the densest of the three. The Talalay process adds two steps to the manufacturing (vacuum sealing and flash-freezing) to create a bouncier foam core. Dunlop Continuous Pour is able to deliver a mid-range bounce and density with a reliable quality across batches. None of the methods produce a superior quality product to the others; in the end, choices come down to personal preference, level of support, and price.
Natural latex foam made by all production methods is breathable, described as hypoallergenic [even though there's no baseline for that term], and anecdotally is resistant to dust mites. As with all quality products, proper care is required. Good ventilation will prevent mold and mildew from forming, and a good mattress protector that you can take off and wash will help keep dust mites at bay. A proper foundation will also extend the usable life of your mattress.
In 1929, Dunlop chemical researcher Eric Owen figured out how to make rubber (think Dunlop tires) into foam. The Molded 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.
Densest of the three types, Molded 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). Molded Dunlop is produced overseas, mostly in Sri Lanka, India, Malaysia and Vietnam. It is not made anywhere in the US, and it is the only manufacturing process of latex foam that sometimes carries organic certification. I've included more insights to certified organic latex below.
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.
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.
Developed in the mid-1940s, the Talalay process is similar to the Molded Dunlop process – up until the part where the foam gets put into the mold. The foam is still made of liquid latex mixed with curing agents and then whipped into foam. In the Talalay process, computers set the amount of latex to be distributed and it is manually piped in and spread into pincore 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 and Dunlop Continuous Pour. 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.
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!
When it comes to durability and performance, Talalay stands up just as well as the others. Sometimes blended Talalay (natural and synthetic latex in combination) has been known to outperform all-Natural latex. All latex is known for its ability to conform to support the body, and then return to its original shape. There will be some softening and sagging over time in the places where you sleep, it is normal and to be expected. Height, weight, moisture and heat are the elements that fatigue a mattress. With a Spindle latex mattress, the warranty covers sagging or compression of greater than ¾ of an inch. While most innerspring mattresses provide warranties after 1.5 to 2 inches of compression or sag, Spindle’s warranty covers its latex mattresses with a sagging or compression of greater than ¾ of an inch!
For all natural latex, the manufacturing process takes about 90 – 105 minutes from pour to cut. Talalay may take a bit longer, as the method has a couple more steps and their drying process is extensive. It is interesting to note that 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.
The third production method used to make latex foam cores is called Dunlop Continuous Pour. This is the process Spindle uses to produce the latex layers for our mattresses. There are only two manufacturers of Dunlop Continuous Pour in the US. We use latex foam made by Mountain Top Foam in Mountain Top, PA.
After mixing in big tanks, Dunlop Continuous Pour latex is (you guessed it!) poured in a continuous stream onto a conveyor belt and smoothed end to end by a mechanical arm. At this stage the foam is the consistency of soft serve ice cream. It is given some time to gel, and a series of tests for temperature, weight and consistency are all performed to make sure the mixing tanks have done their job properly.
Once it is assured that the foam is the right consistency, a machine inserts a mold (with pins in it) from above into the poured latex. If the line is a 6” pour, both the top mold and the bottom of the conveyor belt have pins. In the 3” premium line, which we use for Spindle mattresses, the bottom is smooth and the top of the mold has pins. The molds descend, one after the other, as the line moves forward.
Next the line passes through the infrared treatment, which helps to set the latex before it enters the vulcanizer. The vulcanizer is basically a big steam oven that cooks the latex and turns the liquid foam into a solid. After 30-45 minutes, the line leaves the vulcanizer. The molds are removed by a mechanical arm that drops down, lifts the mold straight up, and swings it back to the beginning of the line. The line of continuous latex is washed/sprayed with clean water three times and then put through a water extractor so all the water is squeezed out. Then it hits the dryer. After it leaves the dryer, it is cooled by fans and cut to size with a mechanized side-to-side saw.
As with each manufacturing process, the foam is subject to ILD and compression testing to ensure quality and consistency. With the continuous pour process, each piece is cut to size so there is no need for glue seams anywhere within the Continuous Pour layers.
While Talalay is known to be light and bouncy and molded Dunlop is denser, continuous pour is somewhere in between; though maybe slightly on the denser side of the scale. It offers excellent support with a little more bounce than original molded Dunlop but far from as "woobly" as Talalay. A real benefit to Dunlop continuous pour is the way it reduces motion transfer, so you don’t have to worry about waking your partner every time you move. Because it is poured in a constant stream, each piece is cut to size with no need for seams or glue anywhere. Continuous pour also offers a new opportunity to create thinner layers of latex. Rather than cutting a 6 inch block in half from top to bottom, continuous pour can be adjusted to 3 inches or even half an inch, for use in customizing comfort within a mattress cover or as a topper. The durability, breathability and support is all still there, and with proper support and covering, your latex mattress is resistant to mold, mildew, dust mites and other allergens.
Latex used to be made primarily by two methods, Dunlop or Talalay. The difference lies in the process by which the liquid latex is transformed to a solid; different processes result in different feels.
Traditional molded Dunlop vulcanizes the latex in molds until the foam becomes solid. Talalay has a more extensive (and more resource intensive) process of vacuum sealing, flash freezing and then baking its molds. The attributes of each process are reliably consistent, yet produce different feeling latex foams. Dunlop molded latex foam is known for its solid support, with the least variation in firmness. The Talalay mold results in a latex foam that is considered to be a “bouncier” latex that is less dense, or more flexible, with a greater variation in softness and hardness.
A third process came along in the 1980s called Dunlop Continuous Pour. That’s what we use for all our Spindle mattresses and it’s manufactured in Pennsylvania by Mountain Top Foam. This latex is what we call an “in-betweener” latex foam, with a feel somewhere between Dunlop and Talalay, but leaning slightly more in the molded Dunlop direction.