The state of the art defense in product liability is an affirmative defense that lets a manufacturer avoid liability by showing its product matched the best scientific and technical knowledge available when the product left its control. The underlying question is simple: could anyone, working with the research, engineering, and materials of that era, have made the product safer in a feasible way? If the answer is no, the manufacturer argues it should not be punished for a harm no one could have prevented. How much that argument is worth depends on the state where the case is filed, whether the claim sounds in negligence or strict liability, and whether the alleged problem is a design flaw or a missing warning.
What the Defense Actually Requires
The defense looks at what was scientifically and technically feasible when the product left the manufacturer’s control. Courts consider the full body of knowledge available to experts in the relevant field at that moment: scientific literature, patent filings, academic research, and the engineering capabilities of the time. It is not limited to what one company happened to know.
Feasibility is the practical half of the test. A manufacturer may be able to show that a safer concept existed in a laboratory setting but could not be built into a consumer product without making it unworkable or prohibitively expensive. Courts separate what a researcher might have speculated about from what an engineer could actually put on a production line.
Because this is an affirmative defense, the manufacturer carries the burden of proof. That generally means producing documentation from research and development, expert testimony about the limits of the era’s technology, and evidence that the design reflected the best available science. In some jurisdictions, once the manufacturer meets that initial burden, the plaintiff must then show the product failed to conform to what was technically feasible.
Industry Custom Is Not the State of the Art
One of the most common mistakes in product liability litigation is treating what competitors were doing as the same thing as what was scientifically possible. They are different standards. Industry custom reflects actual practice. The state of the art reflects available knowledge. An entire industry can lag behind the science, and matching your competitors does not protect you when it does.
The principle traces to a 1932 federal appellate decision holding that an entire profession’s failure to adopt available safety technology did not excuse any individual member from liability, because “a whole calling may have unduly lagged in the adoption of new and available devices.”1Justia Law. The TJ Hooper, 60 F.2d 737 (2d Cir. 1932) Industry practice can be evidence of reasonable care, but it does not define it.
In practice, this means showing that no competitor used a particular safety feature is not enough. The manufacturer has to demonstrate that no one in the scientific or engineering community had developed a feasible way to make the product safer. Evidence often includes academic journals, patents, conference proceedings, and government-funded research from the manufacturing timeframe. If any of those pointed toward a workable improvement, the defense weakens.
Regulatory Compliance Is Also Not the Same Thing
Meeting a government safety regulation is a separate defense. Regulatory compliance shows the product met the minimum standards set by a federal agency. The state of the art defense goes further and asks whether the product incorporated the best knowledge available, regardless of what regulations required. A product can satisfy every applicable safety rule and still be found defective if superior safety methods were scientifically available and the manufacturer ignored them.
Some states do give manufacturers extra credit for regulatory compliance, usually as a rebuttable presumption rather than a complete shield. Texas law, for instance, presumes a product is not defective if it met mandatory federal safety standards applicable at the time of manufacture that governed the specific risk at issue. A plaintiff can overcome that presumption by showing the federal standards were inadequate or that the manufacturer withheld relevant information from the regulatory agency.
How the Defense Works in Design Defect Cases
The state of the art defense appears most often in cases alleging a product’s design was defective. Under the Restatement (Third) of Torts: Products Liability framework, a design defect exists when the foreseeable risks of harm could have been reduced by a reasonable alternative design, and the absence of that alternative makes the product not reasonably safe. Courts use a risk-utility balancing test, weighing the likelihood and severity of harm against the cost and practicality of a different design.
The state of the art defense attacks the reasonable alternative design element directly. If the scientific and engineering knowledge of the era did not support a safer design that could be practically implemented at a reasonable cost, the manufacturer argues no defect existed in the first place. Courts also consider the probability and seriousness of foreseeable risks, the warnings that accompanied the product, consumer expectations, and whether a different design could be used without compromising the product’s core function.
A plaintiff who cannot point to a concrete, feasible alternative design that existed during the relevant time period will have trouble establishing a design defect at all. The manufacturer’s job is to show the jury that its engineers worked within the real constraints of materials, manufacturing processes, and cost that defined the era, and that no one had a workable solution to the problem that eventually caused the injury.
How the Defense Works in Failure-to-Warn Cases
The defense also applies to claims that a manufacturer failed to warn about a product’s dangers, and this is where the law splits most sharply.
Most jurisdictions allow the defense in failure-to-warn cases. The logic is that you cannot warn about what you cannot know. If no scientific method could have identified a particular risk when the product was sold, the manufacturer had no basis for a warning. This argument is common in cases involving long-term chemical exposure, pharmaceutical side effects, and materials later discovered to be harmful. Manufacturers typically present expert testimony showing the scientific literature of the era did not recognize the risk.
A minority of courts have rejected this reasoning when the claim is brought under strict liability. The most prominent example is a 1982 New Jersey Supreme Court decision involving asbestos, which barred the state of the art defense in strict liability failure-to-warn cases. The court reasoned that strict liability focuses on the product, not the manufacturer’s knowledge, and that the cost of injuries from dangerous products should fall on the manufacturers who profit from them rather than on victims who had no way to protect themselves.2Justia Law. Beshada v Johns-Manville Products Corp (1982) This is a minority position, but it shows how much the defense’s availability can shift depending on jurisdiction and legal theory.
Strict Liability vs. Negligence
How the defense operates also depends on whether the claim is brought under negligence or strict liability. In a negligence case, it fits naturally. Negligence asks whether the manufacturer acted reasonably, and showing the product reflected the best available knowledge is powerful evidence of reasonable conduct. If no one in the field knew about a risk, failing to guard against it was not unreasonable.
Strict liability is different. In theory, it imposes responsibility regardless of the manufacturer’s level of care, asking whether the product was defective rather than whether the company was careful. The state of the art defense creates tension with that framework because it reintroduces questions about what the manufacturer could have known. Some jurisdictions resolve the tension by allowing the defense as evidence relevant to whether the product was defective. Others, following reasoning like the New Jersey asbestos decision, reject it as incompatible with strict liability’s focus on the product itself.
The practical result is that the same product and the same injury can produce different outcomes depending on the legal theory the plaintiff chooses and the court where the case is filed.
How States Treat the Defense
State legislatures have taken a range of approaches to codifying the defense, and the differences matter for both sides. The treatments generally fall into three categories.
- Complete bar. In some states, the defense is an absolute shield. Arizona’s product liability statute provides that a manufacturer is not liable if the product’s design, manufacturing methods, and testing conformed to the state of the art when the product was first sold. If the manufacturer proves it, the case ends.
- Rebuttable presumption. Other states presume the product was not defective if its design and manufacturing conformed to the prevailing state of the art, while letting the plaintiff overcome that presumption with contrary evidence. Kentucky uses this approach, presuming non-defectiveness when design, manufacturing methods, and testing met generally recognized standards or the state of the art at the time.
- Admissible evidence. In states that have not codified the defense as a bar or presumption, state of the art evidence is still admissible for the jury to weigh. The manufacturer can present it, but the jury is free to find liability under a different theory.
Statutory language shapes everything from what the manufacturer must prove to what the plaintiff can argue in response. Some statutes fix the relevant timeframe at when the product was first sold by the defendant; others tie it to when the product was manufactured. A few states have rejected the defense in certain contexts. The specific statute in the jurisdiction where the lawsuit sits is the starting point for either side.
Federal Preemption as a Separate Shield
When a product has been approved by a federal agency, manufacturers sometimes argue federal law preempts state product liability claims entirely, which can be stronger than the state of the art defense. The U.S. Supreme Court addressed this directly for medical devices in Riegel v. Medtronic, holding that the Medical Device Amendments Act bars state common-law claims challenging the safety or effectiveness of a medical device that received premarket approval from the FDA.3Justia. Riegel v Medtronic Inc, 552 US 312 (2008) Once the FDA has reviewed and approved a specific device design, state law cannot impose requirements “different from, or in addition to” the federal ones.
The Court left an opening. State claims that parallel federal requirements are not preempted. If a manufacturer violated an FDA regulation and that violation caused the injury, a plaintiff can still pursue a state-law damages claim. Preemption blocks only claims that would require the manufacturer to do something different from what the FDA approved or mandated.
In practice, a manufacturer may raise state of the art as the primary defense, regulatory compliance as a secondary argument, and federal preemption as a threshold argument that could end the case before a jury hears anything.
What Happens When Science Catches Up Later
The defense protects manufacturers based on what was knowable at the time of sale. Science does not stop there. When new research reveals that an older product carries dangers that were previously undetectable, the question becomes whether the manufacturer has a continuing duty to act.
The Restatement (Third) of Torts addresses this through a reasonable seller standard. A manufacturer may face liability for failing to provide a post-sale warning if a reasonable person in the seller’s position would have done so. The analysis looks at four factors: whether the seller knows or should know the product creates a substantial risk of harm, whether affected users can be identified and are likely unaware of the risk, whether a warning can be effectively delivered, and whether the risk is serious enough to justify the cost of warning. This duty can arise even if the product was not defective at the time of sale.
A narrower approach, followed in some jurisdictions, limits post-sale obligations to situations where the manufacturer later learns the product contained a latent defect at the original sale. Under that standard, new discoveries about general risks tied to a product type may not trigger any duty. The practical effect is that a manufacturer that successfully used the state of the art defense at the time of sale may still face liability years later under the broader standard if new research changes the picture and the company does nothing.
The Role of Expert Testimony
The defense lives or dies on expert testimony. The manufacturer needs witnesses who can credibly explain what scientists and engineers knew during the relevant period, what tools were available, and what designs were achievable. The experts involved often include mechanical and design engineers, materials scientists who can speak to the properties and limitations of the materials of the era, human factors specialists who address warnings and consumer safety, and accident reconstruction experts who tie the product’s design to the injury.
Courts control which experts the jury hears through admissibility standards. Most federal courts and many state courts apply the framework from Daubert v. Merrell Dow Pharmaceuticals, which evaluates whether the expert’s methodology can be tested, has been peer reviewed, has a known error rate, operates under standards and controls, and has gained general acceptance in the scientific community. A minority of states still follow the older Frye standard, which asks only about general acceptance in the relevant field.
For the state of the art defense, this analysis matters more than usual because the entire argument depends on reconstructing the state of scientific knowledge at a specific point in history. An expert who cannot show a reliable methodology for doing that is likely to be excluded, and with that testimony often goes the defense itself.