Studies were conducted to investigate what protective nature the cocoon and nylon carpeting has against the performance of insecticides directed at cat flea, Ctenocephalides felis (Bouché), pupae developing in carpet. The following 5 combinations of life stages and substrates were used in these tests were: (1) larvae that pupated in carpet, (2) cocoons placed in carpet, (3) naked pupae placed in carpet, (4) cocoons placed on filter paper, and (5) naked pupae placed on filter paper. These studies evaluated the performance of chlorpyrifos, microencapsulated chlorpyrifos, propetamphos, permethrin, and linalool. When averaged over all insecticides, the mean controls of cocooned pupae placed in carpet and cocooned pupae placed on filter paper were 37.2 and 26.7%, respectively, whereas that of naked pupae placed in carpet was only 13.7%. Additional tests conducted using chlorpyrifos revealed that mortality was 23 and 42% higher, respectively, whenever pupae in cocoons and naked pupae were treated in glass dishes without filter paper. These studies demonstrate that the debri-coated cocoon is not a barrier to insecticide penetration, and that pupae appeared to be protected inside the carpet matrix. Additional studies demonstrated that control of pupae developing in carpet was maximized at lower application pressures. The mean control of pupae with chlorpyrifos at 0.7 kg/cm2 pressure was 77.2%, yet applications at 1.7 kg/cm2 resulted in only 23.3% control.