The moisture uptake of polymers and composites has increasing significance where these materials are specified for invasive, long-term medical applications. Here we analyze mass gain and the ensuing degradation mechanisms in phosphate glass fiber reinforced poly-epsilon-caprolactone laminates. Specimens were manufactured using in situ polymerization of epsilon-caprolactone around a bed of phosphate glass fibers. The latter were sized with 3-amino-propyltriethoxysilane to control the rate of modulus degradation. Fiber content was the main variable in the study, and it was found that the moisture diffusion coefficient increased significantly with increasing fiber volume fraction. Diffusion, plasticization, and leaching of constituents appear to be the dominant aspects of the process over these short-term tests. (C) 2007 Wiley Periodicals, Inc.