Evidence of industry custom and practice generally is not admissible in a  design defect products liability case to show that the manufacturer acted reasonably in adopting the challenged design, nor to show that the product’s design is safe since all manufacturers may be lagging behind reasonable safety standards.  However, industry custom and design may be admissible, though not determinative, in connection with other Barker v. Lull factors in assessing risk vs. benefit of the design, such as whether the product is as safely designed as it should be, considering the feasibility and cost of alternative designs.

California Supreme Court (Kruger, J.; Dato & Liu, JJ., concurring); August 27, 2018; 6 Cal. 5th 21