A series of examinations of the 82 samples found that 32 (38 percent) had multilayered backings. The same manufacturer did not produce all of the tapes with multilayered backings. Thus, identifying the tape manufacturer in order to direct investigators toward a likely origin of a duct tape evidence sample may not be possible solely through backing analysis. These findings have caused the FBI Laboratory to modify its standard operating procedure for duct tape analysis. Microscopic examinations are now performed on duct-tape-backing cross-sections in order to identify any possible layers. The protocol has been modified to include Fourier transform infrared spectroscopy (FTIR) analysis with an attenuated total reflectance (ATR) accessory applied to both sides of the backings. These analyses may lead to discrimination between two samples that may not have been differentiated otherwise. Even when no differences are found, the layer structure may influence the sample preparation for subsequent analyses. The 82 duct tape samples represented tapes that could be easily obtained by consumers and thus were comparable to casework evidence submitted to the FBI Laboratory. Prior to analysis, the adhesive layer of each of the samples was removed with a suitable solvent, and the reinforcement fabric was removed manually. Three different methods were used to evaluate the duct tape backings: macroscopic examination, manual cross-sectioning, and FTIR-ATR. 5 figures and 4 references