Latex is a terrific product. It is very dense (typically 4 lb/cubic foot density) and a quality mattress core of latex will last virtually forever. Latex mattress cores (this is the industry term for the piece of latex used to make the mattress and they tend to be 5" or 6" thick) are always made with holes in them (called pincore holes) - these holes soften the latex and make it comfortable. The larger the holes, the softer the latex core will feel. Most latex mattresses just have one size of holes through the whole mattress so the mattress has a uniform feel throughout. Some cores, though, are made with different sections of latex with different sized holes. This allows the bed to have different zones - softer under the shoulders and feet and firmer under the hips. Finally, many latex beds layer other materials (whether softer latex or memory foam, etc) on top of the latex core to give the bed a softer or more yielding feel. Latex mattresses have a nice bouncy feel and they are very supportive. I think that latex makes a great core and is a big improvement over inner springs and denser and more substantial than foam cores.
What is latex, though? Originally it was just natural rubber that was made of the sap of actual rubber trees. And latex is still made this way today. But during WWII, scientists also learned how to create synthetic latex. I don't claim to understand the chemistry behind all this, but manufacturer's tell me that synthetic latex has the same properties as natural.
Today, most latex mattresses tend to be either made of synthetic latex or more typically a combination of synthetic and natural latex. The manufacturer's of these combination latex mattresses that I talked with claim that a combination makes the whole latex core more resilient. Of course, the all natural latex manufacturers said this was rubbish - that an all natural product is just as resilient and is actually made of natural rubber (as opposed to petrochemical synthetic latex). To a degree I think that it is just a matter of costs - synthetic latex may be cheaper and so more cost effective to use in a mattress. Are there advantages to going natural latex over the synthetic? I can't say that the quality of the mattress will differ, but I just have a personal preference to the natural rubber from a tree as opposed to a synthetic. This may just be my aesthetic taste, but I just lean toward a natural product over a synthetic copy all things being equal. But be warned - you may pay more for the natural latex mattress and also find that finding an all natural latex mattress is difficult. Although this may be changing since one of the big manufacturers, Latex International, is coming out with an all natural Talalay mattress in the near future.
This raises the second way latex mattresses can be different - the manner in which the cores are made. There are two ways they are manufactured: 1) The original method, called the Dunlop method, involves first whipping the latex liquid with air to make a foam, then pouring the latex liquid into a mold and heating it till it vulcanizes, and 2) the Talalay method, which is a bit more involved. In the Talalay method, the latex foam a vacuum is placed on the mold and other processes are involved that some claim produces a foam that has a more consistent cell structure. The foam, in either process, once made is then washed a number of times to get rid or excess soaps and proteins that can make the foam degrade early and also reduces the rubbery smell of latex.
So, in addition to having two different kinds of latex to choose from (natural or synthetic), you also must determine which method of production (Dunlop method or Talalay method) to choose from as well. Which is best? From my experience at trade shows and in discussions with manufacturers and seasoned latex bed owners, it depended on who you talked with. Manufacturers who used the Talalay method, described their product as being less dense, having more air dispersed in the product due to the flash freeze step used in the process, and claimed that it had a more uniform cell structure. Those who used the more straightforward vulcanization technique in the Dunlop method liked the more elastic, springier feeling it creates, and had strong opinions about using all natural materials. My take: I think they are both good products, but I leaned toward the Dunlop mindset since the technique was developed using all natural latex without synthetic ingredients, and it offered I think a more stable product with some solid history behind it. It turns out Sears sold an all natural Dunlop method latex mattress back in the 50's called the "Harvest House" bed, and many are still in homes even to this day. I have spoken to people who have found these mattresses to be in pristine condition, even after 40-50 years. The Talalay method is promising, both with synthetic and even all natural ingredients, but the technique has not been used as long to really evaluate the longevity of the product when made this way.
So after looking at all the flavors, I tended toward natural, using the Dunlop method because it seemed more straightforward and simplistic in its recipe, able to stand the test of time, something more difficult to find these days, and I felt it had a livelier, more responsive feel than the other latex varieties, including all synthetic and synthetic and natural blends.