Yes indeed. QUL-certified mattresses do not contain any form of synthetic latex.
Latex mattresses can be made of natural rubber latex or synthetic rubber latex.
Natural latex is harvested from the rubber tree Havea Brasiliensis by scratching the bark and 'milking' the tree.
Synthetic latex (Styrene Butadiene Rubber (SBR)) is basically made out of oil. It's a man-made copy of natural latex. The combination of natural and synthetic latex is called ‘blended latex’. Unfortunately, it can also be called 'natural latex' since this not a registered conception. Unlike "organic" or "eco", the term "natural" is not protected by law. Any mixture of natural and synthetic latex = blended latex may be named 'natural latex'. The addition of synthetic latex is customary because it is hardly exposed to environmental influences and thus always behaves calculably during foaming. Experts like the producers of QUL-certified mattresses are of cause able to handle the more delicate latex derived from the plant and do not add any synthetic latex. QUL- Naturlatex mattresses, according to the association, consist exclusively of natural latex. In QUL natural latex mattresses, 100% natural latex is processed. So this is the real natural latex - with no synthetic replacement added.
Like usual in the production of latex mattresses, auxiliaries are also used in the processing of natural latex, otherwise the latex would remain liquid and could not be turned into foam. This remedy (sulfur) is falsely often referred to as chemistry, but is of natural origin. However, since "nature" does not automatically mean "harmless" or "safe", the strict controls of the QUL also include the sulfur compounds arising during vulcanization.