Types of product defects, explained.

Design defects

The product is unsafe as designed, even when manufactured correctly to spec. Examples: a vehicle with a center of gravity that promotes rollover, a power tool without an inexpensive guard, a hip implant with a metal-on-metal articulation that sheds particles.

Test (majority — Restatement Third): Risk-utility. The foreseeable risks could have been reduced by a reasonable alternative design. Plaintiff typically proposes a feasible alternative.

Test (minority — older Restatement Second): Consumer expectations. The product is more dangerous than an ordinary consumer would expect.

Manufacturing defects

A flaw introduced in production — the product deviates from its intended design. Examples: a brake line installed improperly on one vehicle in a production run, a single batch of pharmaceuticals contaminated, a tire with a tread separation from a curing-process error.

Test: Strict liability under Restatement Third § 2(a). The plaintiff need only show the product deviated from its intended design and the deviation caused the injury. The defendant's reasonable care in manufacturing is irrelevant.

Warning defects (failure to warn)

The product's warnings or instructions are inadequate to allow safe use. Examples: a medication without an adequate warning of a known side effect, a chemical without first-aid instructions, a power tool without a clear hazard warning.

Test: Restatement Third § 2(c). The warning is inadequate when the foreseeable risks could have been reduced or avoided by reasonable instructions or warnings. Plaintiff must show that an adequate warning would have changed conduct (read-and-heed presumption helps in many states).

Mixed-theory pleading

Most product cases plead multiple theories. A defective drug case often alleges both design defect (the formulation is too dangerous for its benefit profile) and warning defect (the label did not adequately warn of the known risk). The theories can survive separately on summary judgment, giving the plaintiff multiple paths to trial.

Defenses

• State of the art: the product was as safe as the available science permitted at time of sale.
• Unforeseeable misuse: plaintiff used the product in a way the manufacturer could not have anticipated.
• Comparative fault: plaintiff's own conduct contributed to the injury.
• Learned intermediary: warning ran to the prescribing physician, not the patient.
• Statute of repose: hard cutoff from date of sale.