In Borg-Warner Corp. v. Flores, 232 S.W.3d 765 (Tex. 2007), an automobile mechanic sued Borg-Warner and others claiming that the dust generated by the grinding of asbestos-containing brake pads caused his asbestosis. 232 S.W.3d at 766. In reviewing the intermediate appellate court's determination that Flores had brought forward legally sufficient evidence of causation at trial, the supreme court considered the appropriate causation standard to be applied in cases in which a plaintiff "claims to be injured by an asbestos-containing product." Id. at 768-69. The court held that in such cases, "we must determine whether the asbestos in the defendant's product was a substantial factor in bringing about the plaintiff's injuries." Id. at 770. Because "exposure to asbestos, a known carcinogen, is never healthy but fortunately does not always result in disease," a plaintiff must prove more than exposure to an asbestos-containing product to prove that a particular product was a substantial factor in bringing about his or her injuries. Id. at 770-71. To prove "substantial factor causation," a plaintiff must show both frequent, regular, and proximate exposure to the product and reasonable quantitative evidence that the exposure increased the risk of developing the asbestos-related injury. Id. at 769-72. In that case, the plaintiff's expert identified a treatise that discussed the asbestos-related risks to brake mechanics and testified that a 1968 article explained that respirable fibers remain after the braking process so that brake mechanics can be exposed to them. Id. at 767. The evidence was insufficient because there was "no evidence of the approximate quantum of Borg-Warner fibers to which Flores was exposed, and whether this sufficiently contributed to the aggregate dose of asbestos Flores inhaled, such that it could be considered a substantial factor in causing his asbestosis." Id. at 772.