Borg-Warner Corporation v. Flores, 232 S.W. 3d 765 (Tex. 2007), involved occupational exposure to brake linings containing embedded asbestos fibers. Id. at 773-774. Noting that there must be evidence that the exposure was sufficient to exceed some threshold, referencing the ambient air level but without adopting it as the threshold, the court held as a matter of law that the evidence was insufficient to establish causation because it failed to demonstrate that the exposure to asbestos fibers emitted by the defendant's products was more than de minimus. Id. The court noted that it had not adopted the frequency, regularity, and proximity test to determine substantial factor causation, and did not state how it differed, if at all, from Texas law, but appeared to conclude that the result would be the same under either that test or Texas law. Id. at 770, 773-774.