Hydrocolloid wound dressings (HWDs) are used extensively in the treatment of skin trauma. They have laminated structures consisting of an inner (hydrocolloid) layer which absorbs wound exudate and an outer layer (typically polyurethane) which acts as a rate limiting barrier and provides mechanical strength. Water vapour transmission is an important performance parameter and for HWDs the transport process is complicated by the swelling of the hydrocolloid layer. A model was developed to predict this process and takes into account concentration-dependent diffusivity and solubility, moving boundary and convection effects. A finite difference solution to the model was obtained and validated by experiments on a widely used HWD, Duoderm CGF. A parametric study was carried out and it was found that the most sensitive parameters were the diffusivity and solubility of the hydrocolloid layer. It is expected that the model developed and the results obtained will further the knowledge of water vapour transport within wound dressings and will assist in material selection and design of new dressings.