Michael Mavroudis worked for the United States Navy doing ship conversions. Mavroudis spent almost four years on a project converting the U.S.S. Wright in the Puget Sound Naval Shipyard. As part of that project, Mavroudis used three types of insulation, each made of asbestos. One of the insulations, Kaylo, was manufactured by the Owens-Corning Fiberglass Corporation (OCF) (defendant). Shortly after retiring, Mavroudis was diagnosed with mesothelioma, a disease exclusively associated with asbestos exposure. Mavroudis sued OCF, alleging, among other things, that OCF negligently failed to warn Mavroudis of the danger posed by Kaylo. Mavroudis died after filing suit, and his personal representative, Denise Mavroudis (plaintiff), was substituted as the plaintiff. At trial, an expert witness testified that all of Mavroudis’s exposure to asbestos from the various insulations he used at the Puget Sound Naval Shipyard had probably contributed to Mavroudis’s mesothelioma. The witness also testified that he could not determine which of these asbestos exposures were the actual cause of the disease. Finally, the witness testified that even just 10 percent of Mavroudis’s exposure level would have been enough to cause mesothelioma. In regard to the question of causation in fact, the judge instructed the jury that the plaintiff did not have to prove that but for Mavroudis’s exposure to Kaylo, he would not have developed mesothelioma. Instead, the plaintiff had to prove that Kaylo was a substantial factor in Mavroudis’s illness, even if Mavroudis would have become ill regardless. The jury found in favor of Denise Mavroudis and awarded damages of over $1 million dollars. OCF appealed, arguing that the trial court improperly instructed the jury in regard to causation.