From The Mattress Underground -
"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)."
"Latex comes in a natural and synthetic version (this is outside of how it's made because any manufacturing method (Dunlop or Talalay) can use natural, synthetic, or a blend of latex rubber). Chemically they are a very similar molecule however natural latex also includes other ingredients in small quantities which contribute to its qualities and in general is a superior form of rubber in the properties that are most valued in latex."
"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. SBR (Styrene Butadiene Rubber or synthetic latex) does have some properties however that can be superior to NR (Natural Rubber latex) in some of its formulations which is its ability to resist heat aging, abrasion resistance, and softening (which in some combinations can reduce body impressions). It is also less expensive which is one of the reasons for its more common use. For this reason, a blended latex, often found in Talalay latex especially, may be more durable than the purely natural version of Talalay, particularly in the less dense very soft ILD ranges."