Hi LookingNow,
When two substances are chemically bound together then they are different from either one individually. For example water is a chemical that is composed of hydrogen and oxygen that are chemically bound together.
Salt is also a chemical that is made from sodium and chlorine and chlorine by itself is also toxic by itself but isn’t toxic when it is chemically bound to something else.
Styrene butadiene is a copolymer of styrene and butadiene that are chemically bound together.
All the latex you are likely to encounter (Dunlop or Talalay and made from natural or synthetic rubber or a blend of both) will have been tested for harmful substances and VOC’s by either Oeko-Tex Standard 100 or by Eco-Institut using some very stringent testing protocols (see post #2 here) and would be “safe” for almost everyone with the exception of those who may have unusual sensitivities to the chemicals used to formulate and cure the latex or who have allergies to natural latex itself (see post #2 here for more about latex allergies).
Yes … blended latex is by definition a blend of natural rubber (NR) and synthetic rubber (SBR). The blend would vary but all blended latex will include some percentage of SBR.
I don’t think that either one can be considered to be “safer” than the other because both have been tested with the same protocols for harmful substances and VOC’s. The exception would be if someone had a type 1 allergy to natural rubber then for them synthetic rubber would be safer than natural rubber.
Phoenix