Latex rubber is made from a milky liquid (not the sap) that comes from a rubber tree. This form of latex is called NR which stands for Natural Rubber. It can also be made synthetically from a chemical called SBR (Styrene Butadiene). While the actual latex molecule in both is similar, natural latex has a more complex chemistry and more of the desirable qualities that make latex attractive in mattresses (elasticity, durability, compression modulus, resilience, and others). SBR is also less expensive than natural rubber (NR).
Besides the differences in natural or synthetic raw materials, latex foam is usually made using one of two different manufacturing methods. The first is called Dunlop which produces a denser form of latex. This method is more common around the world as it is a simpler less expensive method of manufacture. When used by a reputable manufacturer, it produces a very high quality latex that is very dense and very elastic. Because in this method of manufacturing some of the latex particles "settle" while it is being made, Dunlop is a little less consistent in softness over the entire surface of the layer. It is also more difficult to make Dunlop in a softer version and it is rarely seen in ILD's (a measure of softness) below the mid 20's (medium soft). This same “settling” can result in Dunlop often being firmer on one side of a layer than the other. This gives it a very high support factor (progressive compression) which is a desirable quality in a support material.
Talalay on the other hand is made using a vacuum method that requires less raw material in its manufacture and results in a foam and cell structure that is more consistent than Dunlop, has a lower density (weight) in comparable levels of softness/firmness, and can be made in softer versions than Dunlop. It is also more “lively” and is often preferred over Dunlop in the comfort layers of a mattress. In its firmer versions it can also be a very desirable material in support layers as well.
The softness or firmness of latex can also be varied by changing the amount of raw material used in the core (in the case of Talalay), changing the size, shape and pattern of the pincore holes in the latex, changing the compounding formula used, or by changing the amount of air in the foam and the size of the cells during foaming. The holes or "pin cores" are used in manufacturing both types of latex to apply heat to the inside of the latex in the mold to cause it to set or cure after it is foamed. While the holes are a necessary part of production, the ability to change the qualities or softness of the latex being made by varying their size and shape is a welcome side effect. Because of its heavier denser nature and its high support factor, Dunlop latex is a popular and a very good choice as a support core material and slightly less popular as a comfort layer material however it can be used very effectively in both and this is really a preference issue.
While both are very durable and not as prone as other foams to premature breakdown and body impressions, even in softer versions, there are many in the industry including one of the largest manufacturers of Talalay latex who believe that in the very softest ILD's, Talalay latex that is made completely of natural rubber may not be quite as durable or resistant to impressions as the blended version. This is because Talalay is lighter by nature than Dunlop latex and in ILD's that are very low, blended Talalay may be a preferable choice. It is also less expensive than NR Talalay. Because of the heavier density of Dunlop latex, blends are not necessary or even desirable in any ILD’s.
Talalay latex has a high support factor of about 3 and Dunlop is even higher in the range of 4 so between them they offer a range of flexibility and qualities that other foams cannot duplicate (most other foams are less than 3). This means that in certain constructions where a softer middle layer is desirable to "help" a thinner comfort layer form a pressure relieving cradle while at the same time becoming firm with deeper compression, they are both a very desirable material. Because of this support factor and its ability to conform to the shape of the body (point elasticity), it is unique in the world of foam. While in the highest quality (and cost) versions, HR polyfoam may approach the support factor of Talalay (with less of its other qualities), they are not yet at an equal level.
The feel of the two latex production methods is also different with the denser Dunlop feeling less lively or "springy", blended Talalay being more springy, and NR Talalay being the most elastic and lively yet. The difference is a matter of preference in feel rather than a difference of "better or worse". Because of its simpler method of manufacture, Dunlop is also less expensive than Talalay and the 100% natural version is comparable in price to blended Talalay. Natural talalay is more expensive than both.
Both natural latex and blended latex are very high quality materials. 100% SBR (synthetic) latex does not usually have the same elasticity, quality or performance as natural or blended latex but will still outperform most other foams. While I would be cautious in choosing it over latex that has a higher percentage of natural rubber or an all natural latex version, the cost benefits compared to more natural latex can make it an attractive option as well and it's a higher quality material than most polyfoam. There are also some newer mostly synthetic continuous pour Dunlop latex materials that are promising and are being made in softer versions than you would usually find with Dunlop latex. Both Talalay and Dunlop latex are suitable for use in either support or comfort layers and which one is used depends on the overall construction of the mattress and personal preference. While they are different, one is not better or more suitable than the other. They are also both suitable for use as either a comfort layer or support layer in combination with any other good quality material or component although I would be cautious if there is more than around an inch or so of polyfoam above any latex comfort layers because this could be a weak link in a mattress. There is more about latex support cores in this article and more about latex comfort layers in this article.
Its down side of course is that it can also be more costly than other types of foam however with some shopping around and with the help of the forum and the sources on this website ... latex can be purchased for far less than the so called latex mattresses that are sold by many major manufacturers. In queen size ... you will begin to see some latex core mattresses with the most "basic" features in the range of $1000 and up and mattresses with synthetic latex or latex comfort layers and polyfoam or even innerspring cores for even less.
Be aware that many retail outlets will label a mattress as being a latex mattress even if it has as little as 1" of latex in its construction. This is completely misleading and is simply an effort to take advantage of the known benefits of latex as a selling point even though there would not be enough latex in the mattress to make a real difference. Only a mattress with a latex core should really be called a "latex mattress" and even here the type of comfort layer should be identified in the "category name" given to the mattress. In general terms a mattress should always be identified by both the main material in its core and in its comfort layers. This type of misinformation is often not an "accident" and some salespeople will "insist" that a mattress is made of latex when it only has a very thin, and probably meaningless layer. This is a place where it can be very important to verify the claims of some retail outlets ... which we of course are happy to help you do in our forum.