In many drug cases, a supplier has supplied the drugs to the user in plastic bags or cling film. A comparison of the plastic bags or cling film in which the seized drugs were found with plastic bags or cling film in the possession of the supplier can provide a match that links the supplier to the drugs in the user's possession. The described methods used by the authors to observe the physical properties of transparent plastic bags and cling film were a polarization table, an optical bench providing a shadowgraph and Schlieren image, and microscopic techniques. The properties identified ranged from the characteristics of the polymer film to the size, shape, and design of the finished product. Both plastic bags and cling films have been examined in casework by the reported methods. Usually bags or parts of bags were compared, or several pieces of cling film were compared with the remnants on a roll of film. In some cases, there was a physical fit between items that provided conclusive evidence to link them. In most cases, the physical properties of the items had to be compared and an assessment made of the link. Four cases presented illustrate the techniques used. 9 figures and 7 references