Product liability: manufacturing defects, design defects and failure to warn

Product liability is the set of rules that decides who pays when a defective product injures someone. Cornell’s Wex encyclopedia, an educational secondary source, describes it as legal responsibility imposed on parties along the chain of manufacture for damage caused by a product, and notes there is no federal products liability law, so the rules vary by state (Wex: products liability).

Most claims fit one of three defect types: a manufacturing defect, a design defect, or a failure to warn. This guide uses California’s official civil jury instructions as a worked example, since they set out what a jury is asked to find for each one.

The three kinds of defect

• Manufacturing defect. Something went wrong in making a particular unit. In California, a product has a manufacturing defect if it “differs from the manufacturer’s design or specifications or from other typical units of the same product line” (CACI No. 1202, 2026 edition). Wex describes these as errors affecting only some units of a line.
• Design defect. The plan itself is the problem, so every unit built to that design shares it. Wex describes it as a flaw that exists before manufacture and makes the product unreasonably dangerous.
• Failure to warn. The product lacked adequate instructions or warnings about a risk. Wex calls these marketing defects. The commentary to California’s instructions quotes a court’s observation that even a flawlessly designed and produced product can become defective simply because a warning is missing (CACI No. 1205).

Strict liability, negligence and warranty

Wex lists three theories a claim can proceed under, depending on the jurisdiction: negligence, strict liability, and breach of warranty (Wex: products liability).

Strict liability focuses on the product rather than the defendant’s conduct. Wex lists defective products as one of the areas where strict liability applies in tort (Wex: strict liability). In California, a manufacturing defect claim asks whether the defendant made, distributed or sold the product, whether it contained a manufacturing defect when it left the defendant’s possession, whether the plaintiff was harmed, and whether the defect was a substantial factor in causing the harm (CACI No. 1201). The commentary to CACI No. 1200 adds that strict liability is not absolute liability: the manufacturer does not become the insurer of the user’s safety.

Negligence asks whether the defendant was careless in designing, manufacturing, supplying, inspecting or otherwise handling the product (CACI No. 1220). California’s instructions allow both theories to be presented in the same case.

Breach of warranty is about what the seller promised. California’s express warranty instruction covers a written warranty, a statement of fact or promise, a description, or a sample or model, and asks whether the product failed to perform as stated (CACI No. 1230). That instruction can also require the buyer to have notified the seller within a reasonable time.

Who in the chain of distribution can be liable

Wex says parties throughout the supply chain can be responsible, including component manufacturers, assemblers, wholesalers and retailers. In California, the commentary to CACI No. 1200 quotes the California Supreme Court: “A manufacturer, distributor, or retailer is liable in tort if a defect in the manufacture or design of its product causes injury” during reasonably foreseeable use.

There are limits. The same California commentary notes that strict liability ordinarily does not apply to transactions whose main purpose is a service, and that a component part maker is generally not liable for injuries caused by the finished product unless the component itself was defective and caused harm. Whether a particular seller or distributor counts is a fact-specific question under each state’s law.

Design defects: consumer expectation vs. risk-benefit

Courts use two main tests for design defects, and Wex names both: the consumer expectation test and the risk-utility test. California uses both, as alternatives.

Under California’s consumer expectation test, the plaintiff must show the product “did not perform as safely as an ordinary consumer would have expected it to perform” when used or misused in an intended or reasonably foreseeable way (CACI No. 1203). The court first decides whether the product is one about which ordinary consumers can form minimum safety expectations.

Under California’s risk-benefit test, the plaintiff proves that the defendant made, distributed or sold the product, that the plaintiff was harmed, and that the design was a substantial factor in causing the harm. The burden then shifts: the plaintiff wins unless the defendant proves the design’s benefits outweigh its risks. Jurors weigh the gravity and likelihood of the harm, the feasibility of a safer alternative design at the time of manufacture, and the cost and disadvantages of that alternative (CACI No. 1204).

Failure to warn

California’s strict liability failure-to-warn instruction asks whether the product had risks that were known or knowable in light of generally accepted scientific knowledge at the time; whether those risks presented a substantial danger in intended or reasonably foreseeable use; whether ordinary consumers would not have recognized them; and whether the defendant failed to adequately warn or instruct, causing harm (CACI No. 1205). For prescription drugs and implants, the instruction provides that the warning runs to the prescribing physician.

Misuse, your own fault, and keeping the product

The directions for use in California’s instructions say product misuse is a complete defense if the defendant proves an unforeseeable abuse or alteration of the product, after it left the manufacturer’s hands, was the sole cause of the injury. Misuse that contributed to the harm without being the sole cause can instead reduce damages through comparative fault (CACI Nos. 1203 and 1207A). How your own fault counts varies by state; see our guide to comparative vs. contributory negligence.

The product itself is often central evidence. In California, a manufacturing defect claim asks whether the defect existed when the product left the defendant’s possession (CACI No. 1201), and a misuse defense turns on whether the product was altered afterward. Repairing, discarding or returning the product can make those questions harder to answer. Our guide to spoliation of evidence explains preservation duties.

Recalls, reporting and deadlines

For consumer products, the U.S. Consumer Product Safety Commission publishes a searchable list of recalls and product safety warnings, including the remedy offered for each (CPSC: recalls). The CPSC also runs SaferProducts.gov, where the public can file and read reports about unsafe consumer products; CPSC staff review the reports (SaferProducts.gov). A recall or report is useful background, but it does not by itself decide whether a specific product was defective.

Deadlines matter. Beyond ordinary statutes of limitations, some states have statutes of repose, which Wex describes as laws that bar claims after an action by the defendant, even if the plaintiff has not yet been injured (Wex: statute of repose). Periods differ by state and claim type. See our guide to civil statutes of limitations.

• Keep the product. Store it as it is, with any parts, packaging and manuals.
• Save proof of purchase. Receipts and order records help identify the seller and the model.
• Photograph everything. Document the product, labels, warnings and the scene of the injury.
• Check for recalls. Search the CPSC recall list for the brand and model.
• Report the incident. SaferProducts.gov accepts reports about unsafe consumer products.

This guide explains general legal concepts and is legal information, not legal advice. Product liability theories, defect tests, defenses and deadlines differ by state and depend on the facts; consult a lawyer licensed in the relevant jurisdiction about a specific situation.