A product with a manufacturing defect is one that is not produced according to its initial design. A defective product could harm a customer and lead to a product liability lawsuit.A manufacturing defect is a deviation from the intended quality and specifications of a product that occurs during the manufacturing process. A defective product is any product that has a flaw or mistake that hinders its usability as it was for. Call our Montgomery County product liability attorneys at 215-822-7575 today! You must prove that the product was defective. The proof you'll need will depend on what type of product liability claim you're making.