A lack of scientific data remains the principal obstacle to regulating cigarette toxicity. In particular, there is an immediate need to improve our understanding of the interaction between smoking behaviour and product design, and its influence on cigarette deliveries. This article reviews internal tobacco industry documents on smoking behaviour research undertaken by Imperial Tobacco Limited (ITL) and British-American Tobacco (BAT). BAT documents indicate that smokers vary their puffing behaviour to regulate nicotine levels and compensate for low-yield cigarettes by smoking them more intensely. BAT research also shows that the tar and nicotine delivered to smokers is substantially greater than the machine-smoked yields reported to consumers and regulators. Internal documents describe a strategy to maximise this discrepancy through product design. In particular, BAT developed elastic cigarettes that produced low yields under standard testing protocols, whereas in consumers' hands they elicited more intensive smoking and provided higher concentrations of tar and nicotine to smokers. Documents also show that BAT pursued this product strategy despite the health risks to consumers and ethical concerns raised by senior scientists, and paired it with an equally successful marketing campaign that promoted these cigarettes as low-tar alternatives for health-concerned smokers. Overall, the documents seem to reveal a product strategy intended to exploit the limitations of the testing protocols and to intentionally conceal from consumers and regulators the potential toxicity of BAT products revealed by BAT's own research. Tobacco industry research underscores the serious limitations of the current cigarette testing protocols and the documents describe deceptive business practices that remain in place.