Hi stockdog,
Blended Talalay latex uses about 30% natural rubber and 70% synthetic rubber in the compounding formula.
As far as I’m aware … the Dunlop uses 100% natural rubber yes (although they would be the most reliable source for this type of information and you will need to talk with them anyway about your firmness choice). Just for the sake of clarity … this doesn’t mean that the only material in any foamed latex layer is rubber because there are also other substances needed in the compounding formula to make the foamed latex core (see post #11 here).
All the latex you are likely to encounter has been tested using the same testing protocols for harmful substances and VOC’s and in practical terms I would treat them all as being equally “safe” regardless of whether it uses natural or synthetic rubber in the formula (see post #2 here).
Phoenix