Hi 1sweetdream,
Most people that would be comfortable with the chemicals that are used to manufacture any memory foam (or polyfoam for that matter) would be fine with foam of either type that was manufactured in North America and/or was CertiPur certified for harmful substances or VOC’s.
There are certainly people that are more sensitive that for health or personal reasons tend to avoid memory foam or any synthetic materials in their mattress or the rest of their household environment completely but this would be a relative minority and can involve a great deal of time consuming and detailed research into some complex, conflicting, and often misleading information about the different types of foam, glues, and fire retardants used in mattresses. For those who are willing to do this type of research to help them answer the question of “how safe is safe enough for me?” then post #2 here and the other links and sources of information that it leads to would be a good place to start but for most people the much simpler process of making sure that the foam is either manufactured in North America or CertiPur certified (or in the case of latex Oeko-Tex certified) would be “safe enough”.
Phoenix