How Dunlop Latex & Talalay Latex Are Made
Learn how latex mattresses are made and what are the differences in each latex manufacturing process.
How Dunlop & Talalay Latex Mattresses Are Made
If you have ever wondered how latex mattresses are made, or what the difference between Talalay and Dunlop are, we’re here to help you out. Dunlop latex is the more prevalent of the two types of latex, with only two of approximately thirty latex producers throughout the world having invested in the technology for the Talalay process. The two steps necessary to develop Talalay, that are missing from the standard process, are the vacuum and freezing processes.
Dunlop Latex or Standard Process
- Least expensive to produce
- Used to produce blended and 100% natural latex for mattresses
When you see a latex mattress advertised as “100% Natural” it will have been produced using the denser, firmer, “DUNLOP PROCESS” 95% of the time.
Talalay Latex Process
- Most expensive of the two methods to produce
- Produces more consistent and durable product
- Produces more springy feel with greater range of firmnesses from very soft to extra firm
Two latex manufacturers currently perform the Talalay process, Latex International and Radium Foam.
These manufacturers produce superior latex in terms of consistency, durability, and comfort in the softer blends. There are only 2 manufacturers using the talalay process: Latex International and Radium Foam. If you are considering buying a Talalay latex mattress, make sure the company you buy from is getting their Talalay from one of these suppliers.
Steps For Latex Mattress Core Production
Latex mattresses have been made for many years and latex foam has a deep history. Before the Second World War, virtually all latex used in production was natural. During WW2 supplies of latex from the Far East were very restricted, hence the search for a synthetic alternative. Scientists tried to copy natural latex (derived from cis-polyisoprene) and largely failed: the latex produced was inferior to the real thing.
Instead, they developed a latex based on a synthetic polymer that behaved in a similar way. The word ‘polymer’ simply means a compound made up of long chains of molecules, each link in the chain being derived from simple chemicals known as ‘monomers’. A number of synthetic latices were developed, the most useful one being made by polymerizing Styrene (a liquid) with Butadiene (a gas) to give Styrene-Butadiene rubber, abbreviated to SBR.
Natural and synthetic rubber have different properties. Natural rubber is very soft and elastic, synthetic rubber gives the foam good hardness and processes better (is easier to work with) in production. Compounders tend to use blends of natural & synthetic to get the best overall properties and to stabilize prices.
When natural rubber is tapped from a tree it is very dilute, the rubber content being only about 30%. It has to be concentrated before use to above 61.5% solids. Of these solids 60.0% is rubber, the remaining 1.5% are compounds that are unique to natural latex (proteins, phospholipids, carbohydrates, amino acids). These unique ingredients are very important in explaining the behavior of natural latex.
Soaps & Potassium Oleate
Potassium Oleate stabilizes the foam mix in the mold so it will not coagulate prematurely in the process. Soaps also assist the latex mixture to foam when air is introduced by the foaming machine.
Foaming of the latex compound continues until the targeted foam density has been reached. The mold is closed and the Talalay cycle begins. A vacuum is applied, which causes the foam to expand to fill the mold completely. The latex is then cooled and frozen into place. A disposable paper gasket prevents latex entering the vacuum lines and a rubber gasket seals the mold from the outside world.
This is the key step in the “foaming process” when the liquid foam becomes solid and has gelled.
In the original Dunlop Process, the foam is set by adding to the wet foam of a small amount of gelling agent (sodium silicofluoride or SSF).
In the Talalay process, the foam is frozen then carbon dioxide gas (an acidic gas) is passed through the foam to lower its pH & set it.
This means that on warming up again the foam does not revert to liquid. The foam at this stage is however very weak and could not possibly be removed from the mold intact. The strength is built in during the next stage & vulcanization.
Sulfur and Vulcanization
Sulfur is added to the mix during compounding. Without sulfur in the production process, the foam would resemble chewing gum and would have little resilience. The double bonds in the rubber molecule are utilized by sulfur, which forms bridges with adjacent molecules, known as cross-linking. This process gives the product its familiar properties of elasticity and resilience.
The process of heating rubber with sulfur is called vulcanization or ‘curing’ and was discovered by Charles Goodyear in 1839. This is a fairly slow process, even at a temperature of +240°F so certain accelerators are required in the production process to make this happen quickly. A very small addition of these reduces the time required for curing from about 25 minutes to about 8 minutes. At the end of this time, the mold is cooled, opened, and the product is removed and sent to the washer.
This removes soaps, ammonia and anything else water soluble, that has served its purpose and is no longer wanted or needed in the product. The removal of these prevents discoloration, odor, and a tacky feeling of the product.
Any double bonds in the rubber which are not used up by the sulfur are at risk from attack by oxygen and ozone in the atmosphere, particularly when catalyzed by the presence of UV light. This is why latex will deteriorate in sunlight. A small amount of ‘antioxidant’ is added to the latex during compounding. This is a substance which is preferentially oxidized (& therefore sacrificed), thus affording some protection to the rubber. Eventually, however, it becomes depleted and deterioration of the rubber then occurs. Latex foam must never be cleaned with solvents (dry-cleaning): this would remove any antioxidant completely, causing rapid deterioration.
Molds and Heat Transfer
Molds are made from aluminum (very good heat transfer properties) and are hollow, with channels within their walls so that a heat transfer fluid can circulate through them.
Since latex foam is a very poor conductor of heat a large number of ‘pins’ are present to enable heat/cold to get into the heart of the foam. The pins create pinholes that are very useful because they make it much easier to remove moisture during the drying process.
And there you have it – your latex mattress is made from a series of steps that takes rubber tree sap and turns it into a soft and supportive sheet of foam with varying firmnesses ready to be bundled into a cover.