Although product liability actions are governed by state tort law, they frequently find their way into federal court on diversity jurisdiction. In such actions, federal law provides the procedural rules and state law provides the rule of decision. Although the distinction between procedure and substance is often clear, it can sometimes be nuanced and unintuitive; for example, statutes of limitations are typically viewed as procedural, whereas statutes of repose are viewed as substantive. In Love v. United States, --- F.4th --- (7th Cir. 2021), 2021 WL 5119342, the Seventh Circuit Court of Appeals provides another such illustration of this nuanced distinction and further guidance on the subject in the context of the admissibility of expert opinions.