Claims have been made that certain "thin" polyolefin clothing insulating materials possess superior insulating capabilities because they consist of extremely fine fibers. In a comparative study, swatches of the usual clothing materials, down, polyester, and polyolefin were examined by a technique that allowed two methods of calculating the insulation value, one across the sample and the second from the inner surface of the sample to the ambient air. The second method produces a value that includes the air layer which adheres to all clothing, increasing the apparent insulation. The thermal insulation of the material, per se, does not change. The data demonstrate that the claims can be made for any thin insulation.