Samples of polyurethane foam used in the manufacture of mammary prostheses were enzymatically treated for a total of thirty days. Papain (a plant thiol endopeptidase which has similar activity to the human lysosomal enzyme cathepsin B) was our enzyme of choice since it has both amidase as well as esterase activity. The experiment was conducted under physiological conditions closely simulating the microenvironment likely to be found around an implanted mammary prosthesis. In our tests, 2,4 TDA was formed during enzymatic attack of this TDI-based polyurethane foam for the first four (4) days, reaching a maximum of 8.3 parts per million. After the initial burst, no further TDA was observed within the limits of detection of the experiment (10 parts per billion). Based on standard risk assessment, this amount of TDA translates into a risk of developing cancer of one in four hundred million.